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ELEMENTS

OF

COMPARATIVE ZOOLOGY

BY

ts NGSLE ¥,, Sib.

Professor of Zoology in Tufts College

SAO DEM Pe LOIN LEVELS ED

NEW YORK HENRY HOLT AND COMPANY 1904

[LIBRARY of CoNgRESS| Two Gopies neédved OV 4 1904 Copyrignt Entry 1G 0 of ‘a Noi Copyright, 1897, 1904, : BY HENRY HOLT AND COMPANY es (si Ca a Ce €CeE eG

ROBERT DRUMMOND, PRINTER, NEW YORK |

PREFACE TO THE SECOND EDITION.

In preparing this edition many changes have been made; every page has been revised and some errors corrected. Several new illustrations have been added and directions for the study of other animals have been inserted. As in the first edition, greater prominence has been given to the vertebrate than to the non-vertebrate forms, since experience has shown that the work has been largely used as an introduction to or preparation for medical studies. The greatest change, however, has been in the separation of the laboratory work from the de- seriptive part of the text. Still, the pedagogica advan- tages of the former arrangement have been maintained by numerous cross-references, while the systematic portion has a continuity which was lacking in the former edition.

In the illustrations care has been taken to figure noth- ing which is studied in the laboratory. Students have been known to copy drawings rather than to work the details out from the specimen.

Turts CoLtLEeGE, Mass., June, 1904.

PREFACE TO THE FIRST EDITION.

THE present volume is intended as an introduction to the serious study of zoology. It embraces directions for laboratory work upon a selected series of animal types and a general account of related forms. Laboratory guides are somewhat numerous, but general outlines of zoology adapted to beg nners are few. By combining the two, it has been possible to emphasize the comparative side of the subject. A knowledge of isolated facts, no matter how extensive, is of little value in education, excepting as the powers of observation are trained in ascertaining those facts. Nature studies are truly educational only when the student is trained to correlate and classify facts. A considerable experience with students of different ages has resulted in the conviction that it is not sufficient to ask one to compare a grasshopper and a beetle, pointing out their resemb!ances and points of difference; leading questions must be asked. When the student has answered the questions under the headings ‘‘Comparisons’’ in the following pages, he has a tolerably complete statement of the principal characters of the larger groups of the animal kingdom.

Several considerations have had weight in the selection of types to be studied in detail. In the first place, so far as possible, these should be such as are readily obtainable in any locality. But there are certain important groups,

all the members of which are marine. The forms of these V

vi PREFACE TO THE FIRST EDITION.

which have been used can be purchased of dealers in laboratory supplies (see Introduction) at a cost of less than sixty cents per pupil. In the second place, the number of forms studied and the extent to which details of structure are worked out must be such that the work outlined can be done by students of average ability, in the time usually allotted to such work in the ordinary course. Especial care has been taken that time shall not be wasted in working out features of no morphological importance. Counting tail-feathers or fin-rays has no place in elementary zoology.

Again, the work has been made largely macroscopic in character. Microscopes are expensive, and many institu- tions feel that they cannot afford to provide each student with one of these instruments. Then, too, there are enough important facts to be discovered with scalpel and hand-lens. Too many beginners have been lost among cell-theories and drowned in staining-fluids. These prop- erly come after the elements of the study have been mastered.

In order of treatment the author has followed the se- quence which he believes productive of the best results- A strictly logical course would lead from the simple to the complex, but in practice this has not been found as valu- able as the order adopted here.

A number of illustrations have been prepared especially for this work. Most of the others are credited to the author from which they are taken. It may interest some to know that Figures 39 and 123 were engraved for the second part of Agassiz and Gould’s “Principles of Zool- ogy,’’ which was never published.

Turts CoLuecE, Mass., June 14, 1897.

CONTENTS.

PAGE

Perv R ATO CO TDLIO NR ate Nes 2 eye ree Una, lino files ate Yon.’ Bee ge hoa if VEC PUNT STRANGE OI re scale Aeon, Oetkes of Cao tis hs Bane ae ak eee 2 MEGeKIal 1OE WISSCCLION) i>) 28.1. heen dinia a ee cyclen + EEC Te CCM OO KGit a eto seley ies Mian ttnn oe Selle aber any esa ete es wens 10 (fk TEsO UR 2 TUOTRST AN) 2 Ga ea a 15 iS) Oe Se a ea an aD ea a Re 1 DEN SOSLE oo: dele eae ont ce a eee i a 22 POMP AEISOMS RE ee -os cw. et Mer Soran ce ee Geno oF ko, oy eieney 30 TIED, yard cb eee eC ee eee ee pee 32 “PEC SOLE eke PEI as Se, a IR em 41 Won PATISONS emcees ery eb ee Sek wales ee 43

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(OPE GRE ae SD SS ae rr Na Sas eG at nee ne en ee 84 5 UDG OURS Taye, RIN eG coos ka Vater Oat fe 85 TD NEG EPO Oh lat toc NE Un te a CERRO. Ue 86 ES COROTMINALS TOR. sare is th Syne ERIN S28 ooo See chet Ga 87 WomiparisOnS’: <0. 4s (cpr ee Ns Sc slisy ap) eins med 88 SICHUI SCO U fr a aU I OR URERIn kts, LO 2 Sn 89

vill CONTENTS.

PAGE Buattertly si Vice) ee ee eens ee oS Ss 90 Comparisons..7.%) aca 2 «bes a!) fe ee ee 91 Barthworm. 2053 !.05 3k eeu soe Ge Seana elton ee 92 Comparisons. 200i 08 ee oe eee ee ele as 96 Clam! ek SO ee ae Oe NG vie ar 98 OV SUR, isso icin GAG Bole ae Ae ee er 102 Quid. <i hH. cused dant Hey re Selene ae ee 103 Comparisons! . (2... 55. 2s Woe ine eo 108 Starhish. 055 4) Shh Mee oes 110 Sea-urchime. fo eo Ps Se pee eee 115 Comparisons? #22 40.650. ae ses oe ee 118 Sea-anemone) 2.5 “rele Hoe we eee 120 Hy droid: (Pennaria) esa 22 ecko. Shine ee 123 Hy droid, (Clava). 0) bs oo on aa eee 125 Hydroid Medusa........ Bye chr io Sate errr es. - 127 Comparisonss. io. ..0 200. aa ose ooo 128 Spotiges:.. 6000 5 2 es ee Amcebanwn 4/0. vide awk a ee eee 132 Paramecium ,.9 i902 3 Sele hah ela bie oe ee 134 Comparisons, .)./ 5.5 bso) de 6 Te ee ee 136 SYSTEMATIC ZOOLOGY, THE ANIMAL KINGDOM, o0u5)). 25 0 ak oo. Cee 137 PROTOZOA. 3.02254. 23 cae koe ee ee 145 Whizopodar esi Os. ae ee ee ee 147 Iniusoria) yi och ee Pa See Ae i er 149 SPOLOZOS L Goya nts ek Reine LAO ee nein. 151 PUY ON BG ae Cn, Se selecrls G8 rr 152 IEE TA ZONA, (o< ls'n toe red ae date ac 6 aloe ee eee rr 154 SUNTAN ee ee ee ae ig Pacer ek en 5 157 Spongida..:.. 405 a oe ee 158 SUMATMIATY igen wah ale ees eae eee 161 Celentetata: <4 #5 kd nee oe ee ee er 162 Piyidrozoay 05)! % osteo aaa ek ee Mio ee: 165 SCY PMOZOM). (2.6. eas Gta’ whale & sldiaus Mths nk ae 169 Ctenophora ssi. ee aR ee ete ee 174

CONTENTS. ib

PAGE

RICH CSner tir et Gein TN it poate tee meas yi ed bs ee sn oe 178 Piehehmmmbitest re ere tre een ah ce) Mee eet MS 178 Nena mein tmeges hy Soa as i PN aoe eS UN, 182 JA TEU VEIIG PE Rein Reged: URIS a ag cea 0s Oat Malia ak Var aloe A eee, Drea 183 MON SCOLGe Hae. ces crete ee ee ety SR Ne ee ERE sy 189 SSHUVOTUIMEP A Rate Rs one cee Lia Wve et le led iba Pa ee ch Rie sane oe . 190 RICHES Cai Ro NU Sa eee aa ape tes ae a a CG PER ae 193 EE SOON) OMDB ESR UA ee OR ORG ones ee er ere OM TOUR = a ee 197 1B ST EID] OG eB A ete ce eM ee a ge eaten a epee ad EE 197 EN CETS. NEI Be Ne eae OH peat ear ae ee ee aeRO ig 202 Seale OOda very er he ak nie ys Lk as Mein RN Oe 208 rSIULI MST OYSH E20 rahe Ua ac sa A nc eel ee Melee ea ese a 212 JASE SEP OFSVE Paik ol PTI UI cata Rec ae? ed Gn Ke 215 CHP CISUES IEE SE Ae Oe Sey AON an a RR HO UT al (1a 218 RCSIRS TG ni" We Bie eR Rosas 2 Ae REI ha Rar aS UR Zot MER OSrOmaabay is) ose ate a Ske meta) ols BlerstniGon skate ara ane ate ay vise 231 JASEBICIOTAUTG EO ca EPMA can ne RE EU ae aE oe a EW CO a 232 LERSIECEBB ida eee COR gt = ee 230 Chilopoda, pees oy eles es ee weds ence ens Oe Mae REINS 2% 235 EPelteecAO OMA eee ne eat NO AN ee. Ww Eig Nyce he Bea oe Erase 236 SUMUMALY sweet ss 2 heen ated eee Ment er 270

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BN Feat e Loeb aa ie Mee or ay ae at el cos eect d a Romy cH ER Se eae a 290 Cr COSCOMDES So 1 Ga, caer oh eee aaron heen ame sae ees 315 LETSIOSS ee ORs Bele eaten SW.” Lo 10k Onna a 317 EAeraagoailntcieeae ee oh eee RMR RS alc nine We 336

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Vee rnrnet een ine ee a Copa aren Meet pelle Cc er ee TL 363

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x CONTENTS.

GENERAL ZOOLOGY.

PAGE COMPARATIVE PHYSIOUOGY oo. yoke ce eee eee 395 GENERAL MORPHOLOGY. 22.4006 0 6 228 ee eee 403 GEOGRAPHICAL DISTRIBUTION... ..4..5.2.0. 50500 ee 409 GEOLOGICAL DISTRIBUTION, /; 27.2. 1435.540 62 eee 413 IVOLUTION, . 2.42 Sats fe Ee ee 414

ELEMENTS OF COMPARATIVE ZOOLOGY.

INTRODUCTION.

Every true teacher must have his own methods, but some suggestions as to the way in which this book is intended to be used may be of value. In the first place, the laboratory work is regarded as most important, since through it the student is trained in observation—a train- ing utterly lacking in all the non-scientific studies of the school curriculum; and also since by it he acquires an autoptic knowledge of the animals studied. It is believed that every point mentioned in the laboratory directions can be made out by students in the high-school grades.

In case the time be not sufficient to cover all the forms described, some may be omitted, but the writer thinks that any course should include at least the dogfish, teleost, frog, rat, crayfish, grasshopper, earthworm, clam, star- fish, sea-urchin, and sea-anemone.

Each student should make all the drawings called for. Drawing the object seen is one of the greatest aids to observation, and every pupil, no matter how lacking in artistic ability, can make intelligible sketches of all points demanded. These sketches have great value for the teacher, since by their aid one can see at a glance any

2 INTRODUCTION.

errors or difficulties. All questions asked should be answered in the note-book.

At various points are questions grouped under the head- ing ‘Comparisons.’ These questions are based upon the previous laboratory work, and are intended to bring out clearly in the student’s mind the essential points of resem- blance and of difference in the forms studied, and the bearings of the facts discovered. Laboratory work trains the powers of observation; the answering of such ques- tions leads to a systematization of knowledge and an exercise of the reasoning powers. The value of any scientific study les not so much in the number or impor- tance of the facts learned as in seeing the relationships of these facts and the conclusions to be drawn from them. Hence each pupil should be required to hand in answers to these questions and to make the answers as detailed as possible.

Following each list of comparisons is a reference to the pages where a general account of allied forms and a statement of the principal characteristics of the group may be found, thus giving a completeness to the knowl- edge which otherwise would be utterly lacking. In these general statements there are frequent references to the sections where the student has worked out the point for himself. In this way the work throughout will be based upon the inductive method, and finally the animal kingdom will be comprehended as a whole.

EQUIPMENT.

The room used for laboratory purposes should be well lighted and ventilated and should be furnished with running water. There should be receptacles, prefeiably

INTRODUCTION. 3

earthen jars, for waste, and the students should be made to keep everything clean.

The tables for laboratory work should te low (not over 29 inches from the floor), and should afford each student at least 6 square feet of surface. It is best that there should be no varnish upon them, as this makes trouble when alcohol is spilled.

Each student should have the following instruments, etc.:

Scalpel. Hand lens.

Scissors. Jar of alcohol (or formol). Forceps. Note-book.

Two dissecting-needles. Pencils (hard and soft). Dissecting-pan. Drawing-paper.

As the animals to be dissected are small, the instruments should be of moderate size, delicacy being preferable to strength. The dissecting-pans (preferably of copper) should be about 6 by 12 inches, with flaring sides 14 inches in height. The bottom should be covered to about + inch in depth with wax, so that the specimen may be pinned out during dissection. For most purposes it is better if the wax be blackened by lampblack. When possible the dissection should be carried on under water, as this tends to float up and separate the parts. At the close of each dissecting period the specimen should be placed in the jar of alcohol or formol for preservation until the next time. For this purpose the three-pound glass butter-jars with screw-tops are good. Battery-jars . closed with a plate of glass may also be used.

The pencils should be hard (6H, Faber), and the points should be kept sharp with a file or emery-paper. For drawings a smooth, hard-surfaced unruled paper is best, Bristol-board, aside from expense, being preferable. The

4 INTRODUCTION.

drawings: should be in outline only; shading should not be attempted. Frequently the use of colored pencils will make the sketches more intelligible, and for this purpose the following conventional colors may be suggested:

Arterial circulation, red. Venous circulation, blue. Alimentary canal, brown. Liver, green. Kidneys, purple. Reproductive organs, yellow

Nerves, gray.

The laboratory should be provided with an oil-stone for sharpening instruments; a pair of bone forceps * for cut- ting hard substances; a hypodermic and an injecting syringe for injection; a skeleton of at least one representa- tive of each great group of Vertebrates; and at least one good compound microscope. It will also be advantageous to have a small equipment for microscopic mounting, as there are frequent opportunities for the preparation of objects of interest and value for demonstration to the class.

MATERIAL FOR DISSECTION.

The forms selected for study are, so far as possible, such as can readily be obtained in any locality by taking a little pains at the proper season. There are, however, certain groups of animals which occur only in the sea, and represent- atives of these must be obtained from the shore. These marine forms selected are Embryo Dogfish (Acanthias), Squid (Loligo), Sea-urchin (Strongylocentrotus, Arbacia), Starfish (Asterias), Sea-anemone (Metridiwm), Hydroid (Pennaria), and Calecareous Sponge (Granta). The series

* Side-cut pliers will do.

INTRODUCTION. 5)

may be obtained from dealers* at a cost not exceeding sixty cents per student. Orders for these should be placed in the early summer, so that no difficulty or delay may occur later. Much of the other material may be obtained when wanted, but such as cannot be had in the colder months—frogs, tadpoles, snakes, turtles, crayfish, insects, earthworms, etc.—should be collected in the summer and preserved in alcohol or formol for use later. Those which require injection should be so prepared before being placed in the preservative fluid.

Alcohol.—The most important of all reagents. It can be purchased, tax-free, by incorporated institutions of learning upon the fulfilment of certain conditions, which may be learned by application to the Collector of Internal Revenue in the district in which the institution is situated. As it comes from the distiller it is usually about 95% alcohol, the rest being water. This is too strong for most purposes, and for the preservation of material it should be reduced to 70% by the addition of . water. A convenient method of making different strengths of alcohol is as follows: First, with an alcoholometer, find the percentage of alcohol in the supply. Then fill a metric graduate with alcohol to the mark which corre- sponds to the desired per cent. and then add water until the mixture reaches the mark corresponding to the per cent. with which you started. Thus to make 70% from 94% measure out 70 ce of alcohol, then add water until

* Supply Department, Marine Biological Laboratory, Wood’s Hole, Mass; Dr. F. D. Lambert, Tufts College, Massachusetts; H. H. and C. 8. Brimley, Raleigh, N. C.; Supply Department Hop- kins Laboratory, Stanford University, California. Skeletons and rarer forms can be obtained from H. A. Ward, Rochester, N. Y.; Kny-Shearer Co., 225 Fourth Avenue, New York.

6 INTRODUCTION.

the mixture measures 94cc. While not absolutely correct, the result is close enough for practical purposes.

Formol.—This is a 40% solution of formaldehyde, and for use this should be reduced by addition of water to a 2% or 3% solution (7.e., 1 part formol to 49 or 33 parts of water), in which specimens may be kept in good condition for some months. The same care must be exercised as with alcohol to change the fluid frequently while hardening the specimens. Formol has the disadvantage of evaporat- ing readily, and so the jars must be tightly sealed. It also has the disadvantage of freezing.

A second substitute for aleohol is Wickersheimer’s fluid. This is made by dissolving 100 grams of alum, 25 of com- mon salt, 12 of saltpetre, 60 of potassic carbonate, and 20 of white arsenic (arsenious acid) in 3 litres of boiling water. To this, when cold, add 1200 grams of glycerine and 300 of aleohol. Change the specimens once or twice, and keep them in at least twice their bulk of the fluid. This fluid has been highly recommended, but it is now httle used, formol taking its place. }

Injections are made as a means of more readily following tubular structures, especially blood-vessels, and consist in forcing into these tubes colored material which will render them more easily recognized. For many injections simple apparatus may be used. Thus frequently a glass tube drawn out to a point can be filled with the injecting fluid and then, when the end of the tube is inserted into the blood-vessel, the fluid can be forced into the artery or vein by the pressure of the breath or by a large rubber bulb. It is, however, more satisfactory to use the regular inject- ing syringe, sold by all dealers in naturalists’ supplies. These are provided with small tubes (canulas) for insertion into the vessel to be injected, and these are grooved at

INTRODUCTION. 7

the tip so that they may be firmly tied into the artery or vein.

Most of the injections called for in the present work can be made either through the aorta or through the ven- tricle. The ventricle is cut open and the canula is forced through this opening into the aorta, around which a string is passed and tied, thus holding the tube firmly in place. The syringe is then filled with the injecting fluid (see below) and connected with the canula, when a pressure upon the piston will force the fluid into the blood-vessels. Too much pressure should not be exerted, as the vessels are liable to rupture. It is advantageous in many cases to first inject with 2% formol, which washes out the vessels and helps to preserve the specimen. Then the colored mass is employed.

Various injecting fluids have been proposed, but the following are ample for all purposes, and they have, be- sides, the advantage of not requiring heat, which in the case of some forms causes a softening of the walls of the blood-vessels.

Starch Injection Mass.—Grind together in a mortar one volume of dry starch, one of a 23% aqueous solution of chloral hydrate, and one-fourth volume each of 95% alcohol and of the ‘color.’ The ‘color’ consists of equal volumes of dry color (vermilion, chrome yellow, Prussian blue, etc.), glycerine and alcohol. The mixture will keep indefinitely, but requires thorough stirring before use and quick usage, as the starch and color settle rapidly.

Gum Injection Fluid.—Make a rather thick (molasses- like) solution of gum arabic in water; color it with carmine dissolved in ammonia or with soluble Prussian blue, and strain through muslin. With the addition ofa little thymol the fluid will keep well if tightly corked. After in-

8 INTRODUCTION.

jection place the animal in alcohol, which hardens the eum.

By using both injection masses in succession the complete circulatory system may be injected (double injection). To accomplish this, first inject with the gum fluid, colored blue, and then follow with the starch mass colored red. The gum will flow through the finest vessels, but the starch mass will stop at the capillaries.

Study of Vertebrate Brains.—I{ material be abundant the study of the brain and its nerves will be much facili- tated by putting heads of the various forms in the fluid mentioned below a week or two before the dissection is to take place. The fluid, which should be changed two or three times, softens (decalcifies) the bones, and at the same time hardens the nervous structures. It is composed of equal parts of 95% (commercial) alcohol and 10% nitrie acid. The heads should be washed for an hour or two in water before dissection, as otherwise the acid will attack the dissecting instruments.

Miiller’s Fluid is also used for the preservation of brains and nervous matter, but it does not decaleify. In its use the cavity of the skull should be opened so as to permit free entrance of the fluid. It should be changed in twelve hours, one day, one week, and four weeks. It colors all tissues a dirty green. Miuller’s Fluid is com- posed of

SUlpmatesor SOdean. eee ce ane 1 part Biehromate of potash.) 2.5... .. 2 parts Water eet Llc. kts feud epee eee 100-7

Fuchsin is one cf the most easily used stains. It is made by dissolving 1 part of the aniline dye in 200 parts of water.

INTRODUCTION. 9

Alum Cochineal is made by soaking 7 parts of crushed cochineal insects and 7 parts of alum in 700 of water for twenty-four hours. Then boil until the amount is reduced to 400 parts. Allow to stand twenty-four hours, filter, and add a little thymol to keep it from spoiling. This stain has the advantage of not overstaining specimens, Objects may be left in it from twelve to twenty-four hours.

Grenacher’s Borax Carmine.—Two grams of carmine are dissolved in a solution of 4 grams of borax in 100 ce of water. Then 100 ce of 70% alcohol are added, the whole allowed to stand twenty-four hours, then filtered. A convenient method of use is to add about 1 part of the stain to 25 of acid alcohol (100 ce of 70% alcohol plus 5 drops of hydrochloric acid). After staining, place the specimen for a few minutes in 70% alcohol to which a little ammonia has been added.

Picrosulphuric Acid is used for killing many animals without distortion. It is made by dissolving picric acid in water until no more will be taken up, and then adding to 100 parts of the solution 2 parts of sulphuric acid. It is allowed to stand a day, is filtered, and is prepared for use by adding 3 parts of water to 1 of the stock solution. Specimens killed in this fluid are stained yellow, and should be washed in several changes of water before being placed in alcohol or formol. It takes from one to three hours to kill.

Further directions for the preservation of material and for microscopic study and preparation may be found in the various histologies (Stohr, Bohm and Davidoff, etc.) and in Lee’s ‘ Microtomist’s Vade Mecum” (Philadel- phia). Recent methods and improvements are described in the Journal of Applied Microscopy (Rochester) and the Journal of the Royal Microscopical Society (London).

10 INTRODUCTION.

REFERENCE Books.

In the classroom there should be some works of reference and the teacher should have and use others. As an aid in selection of these works the following remarks may be of value:

There are a number of guides for the dissection of ani- mals. One of the oldest and best of these is the ‘‘ Practical Biology” of Huxley and Martin (Macmillan & Co.), which deals with both plants and animals in a thorough manner, although but a few forms are included. Of a somewhat similar character is Dodge’s ‘‘Elementary Practical Biol- ogy’? (Harper & Brothers), which enters more into the physiological side of the forms studied. The “ Practical Zoology’? of Marshall and Hurst (Putnam) is confined solely to animals, which it describes in a thorough manner. Descriptions of more forms of Invertebrates will be found in Bumpus’ “Invertebrate Zoology” (Holt), Pratt’s ‘Invertebrate Zoology”? (Ginn), and Brooks’ ‘ Inverte- brate Zoology’’ (Cassino), the latter treating of the em- bryology of some as well. For Vertebrates there are Parker’s ‘“‘Zootomy’’ (Macmillan), and anatomies of the cat by Gorham and Tower (Putnam), Reighard and Jennings (Holt) and Davison.

For general accounts of the structure of animals, giving general statements for all groups, Jackson’s edition of Rolleston’s ‘‘Forms of Animal Life” (Macmillan) and Gegenbaur’s ‘‘Comparative Anatomy” (out of print; only to be found second-hand) are good. The general struc- ture of invertebrate forms is covered by Lang’s ‘‘Text- book of Comparative Anatomy” (Macmillan), Shipley’s “Invertebrate Zoology’? (Macmillan), McMurrich’s ‘“In- vertebrate Morphology” (Holt), and Huxley’s ‘‘ Anatomy

INTRODUCTION. fet

of the Invertebrates”? (Appleton). Of these Lang’s work is the most detailed; Huxley’s is rather old; Shipley’s is the simplest. The structure of the vertebrates will be found in Wiedersheim’s ‘“‘Comparative Anatomy of the Vertebrates”? (Macmillan), Huxley’s ‘‘Anatomy of the Vertebrates” (Appleton), and MKingsley’s ‘‘ Vertebrate Zoology”’ (Holt).

The development of animals is discussed in the following works: Balfour’s ‘Treatise on Comparative Embryology”’ (Macmillan), Korschelt and Heider’s ‘‘Text-book of Em- bryology” (Macmillan), Hertwig’s ‘‘Text-book of Em- bryology”’(Macmillan), and Minot’s ‘Human Embryology” (Wm. Wood & Co.). Balfour’s treatise is a standard, but is rather old. JKorschelt and Heider deal only with in- vertebrates; Hertwig and Minot only with vertebrates. MeMurrich’s ‘“‘Development of the Human Body” (Blak- iston) is a smaller work treating almost entirely of the development of mammals. |

Within a few years several good general zoologies have been published. Under this head are included works which treat of the structure, development, classification, etc., of animals. Prominent among these are the ‘‘Text- book of Zoology”? by Parker and Haswell (Macmillan) and Kingsley’s translation of Hertwig’s ‘‘ Zoology” (Holt). Larger works are the ‘‘Cambridge Natural History” and a “Treatise on Zoology’? (Macmillan), now in course of publication. The ‘Riverside Natural History”? (Hough- ton, Mifflin & Co.) and the ‘‘ Royal Natural History” are more popular in character. Among the more elementary works maybe mentioned the zoologies of Jordan and Kellogg, Colton, Weysse, and Davenport.

The broader and more general biological principles, without reference to classification and description of forms,

12 INTRODUCTION.

may be found in Parker’s “‘ Elementary Biology” (Macmil- lan) and Hertwig’s “General Principles of Zoology”’ (Holt).

Besides these there are a number of good works treating of special groups of animals. The student at the seashore of our New England States finds Verrill and Smith’s “ In- vertebrates of Vineyard Sound”’ indispensable. This was published in the Report of the U. 8. Fish Commission for 1871-2, but separate copies may be had from dealers in scientific books. A broader range of forms and wider geographical limits characterizes Arnold’s “Sea Beach at Ebb Tide” (Century Co.). Emerton’s ‘Life on the Sea- shore”’ (Cassino) covers much the same ground, but in a more elementary manner. For the identification of vertebrates Jordan’s “‘Manual of the Vertebrates” (Mc- Clurg) is the standard. There are two good works upon molluses, Woodward’s ‘‘ Manual of the Mollusca’’ (London) and Tryon’s “Structural and Systematic Conchology,” 3 vols. (Philadelphia), both wel! illustrated. The insects are well treated in Comstock’s “‘Manual of the Study of Insects’’ (Comstock Pub. Co., Ithaca, N. Y.), Howard’s ‘““Insect Book’’ (Doubleday, Page & Co.), and Hyatt and Arms’ ‘‘Insecta’’ (Heath, Boston). An older work, but still of great value, is Harris’ ‘‘Insects Injurious to Vege- tation’’ (Boston). The butterflies and moths are well illustrated and described in Holland’s “ Butterfly Book”’ and ‘‘Moth Book’’ (Doubleday, Page & Co.).

There are several works dealing with birds. Of these possibly Chapman’s “Birds of North-Eastern America”’ (Appleton) and Coues’ “Key to North American Birds’’ (Estes & Lauriat) are most widely known. “Ridgeway’s ‘“Manual of North American Birds’”’ (Lippincott) is also good, as is Chamberlain’s edition of Nuttall’s ‘Ornithol- ogy’’ (Boston),

INTRODUCTION. 13

There are also several more special works which are of great value in the laboratory or study-room. Among these are Huxley’s “Crayfish” (Appleton & Co.), Ecker’s “Anatomy of the Frog”? (Macmillan), Darwin’s ‘“ Earth- worms and Vegetable Mould” (Appleton) and his “Coral Reefs.” Dana’s ‘“‘Corals and Coral Islands”? (Dodd, Mead & Co.) is a later work. Flower and Lydekker’s ‘‘Mam- malia”’ (Edinburgh) is excellent. The teacher will find much valuable material in the zoological articles in the Encyclopedia Britannica, though these are very unequal in treatment. Some of the best of them have been re- printed in “‘ Zoological Articles’? by Lankester and others Ga. & C. Black).

A dictionary of scientific terms is frequently asked for. Any of the more recent unabridged English dictionaries will contain almost every zoological term one runs across. Several so-called dictionaries of scientific terms have been published, but as yet not one of any value has appeared.

The teacher should remember that science is continually growing, and that text-books and manuals grow old. He should therefore have access to some of the scientific jour- nals. Among those most valuable to the teacher of natu- ral history are the American Naturalist (Boston) and Biological Bulletin (Lancaster, Pa.). Nature (London) and Science (New York) are weekly publications which include all sciences. The Journal of the Royal Micro- scopical Society (London) is valuable, since it contains not only an account of new methods, but summaries of recent investigations in both botany and zoology. Its price is unreasonably high.

‘

PART I. DIRECTIONS FOR LABORATORY WORK.

EMBRYO DOGFISH (Acanthias).

Material—F or each student a specimen of the late embryo of Acanthias, known to the fishermen as ‘dog-fish pups.’ This should have at least the arterial system injected (easiest done by partly cutting off tail behind last dorsal fin and injecting the caudal artery).

One or more slides of the skin of the ‘pup.’ These may be prepared an hour or more before the laboratory period by placing a bit of the skin on a microscopic slide in a drop of glycerine and covering it with a bit of cover-glass. Such preparations are but temporary; permanent mounts which can be used year after year may be made as follows: The piece of skin, + inch square, is placed for 30 minutes in each 95% and absolute alcohols and then in spirits of turpentine. It is then placed for a moment on a bit of filter-paper to remove the superfluous turpentine, placed in a drop of balsam on the slide and the cover-glass applied. Another slide of the decal- ecified skin stained and cut in sections will show other features of the scales. :

GENERAL TopoGRAPHy. Distinguish in the fish anterior and posterior, right and left, back (dorsum) and belly (venter). Is the animal bilaterally symmetrical? 17.e., are the right and left sides alike? Do you recall any

15

16 LABORATORY WORK.

animal without bilateral symmetry? Make out the re- gions, head, trunk, and tail. Is there a neck? Where is the vent?

How many fins do you find? How many are paired and how many unpaired? Are any in the median line of the body? Can the fins be regarded as folds of the skin? The various fins have names. The median fins are the dorsal on the back, the anal on the ventral surface just behind the vent, and the caudal at the end of the tail. Do you find a skeleton in any of these? Is the caudal fin homocercal (with equal lobes) or heterocercal (with unequal lobes)? The paired fins are, in front, the pectorals; behind, the ventrals. Do these compare, in position, with your own limbs?

How many eyes are there, and where are they placed? Are they movable? Are eyelids present? Notice in each eye the colored iris around the black pupil.*

How many nostrils and where are they? Examine carefully and see how the opening is subdivided by a flap of skin. Sketch. Probe with a bristle and see if the nostrils connect with the mouth or throat. How does this compare with what occurs in yourself?

Where is the mouth? Is there a tongue? Do you find any ears? Behind the eyes are a pair of openings, the spiracles; probe and see if they communicate with the throat. On the sides of the neck, in front of the pectoral fins, are the gill-slits or branchial clejts. How many are there?

Draw the fish from the side, natural size, inserting and naming all the parts made out.

* In preserved ‘pups’ the lens may be whitened so that the

pupil appears white instead of black. Colors also fade in alcohol or formol,

DOGFISH. 17

In the prepared slide of the skin, under a low power of the microscope, see the scales, drawing several of them in thier relative positions. Each scale consists of a basal plate bearing an oblique spine (dermal tooth). This type of scale is called placoid. Do the scales overlap?

INTERNAL STRUCTURE.

Open the fish by cutting in the mid-ventral line from the vent forward to just behind the pectoral fins, and then make cross-cuts at either end so that the sidewalls of the body may be pinned out in the dissecting-pan. Fill the pan with water so that all parts are covered.

This lays open the body cavity, or celom; notice that it is everywhere lined with a smooth membrane, the peritoneum. Through this membrane see that the muscles of the body- wall are arranged in plates (myotomes) extending from dorsal to ventral surface.

Trace the alimentary canal. In the front part of the body-cavity is the lhver with two large lobes and dorsal to it the J-shaped stomach. The intestine begins at the end of the J and extends back to the vent. In the intestine recognize a large anterior portion and a smaller posterior rectum, with a blind sac, the rectal gland, near the junction of the two. Cut a bit of the wall from the larger part of the intestine with the scissors and notice the spiral valve in its interior. What function can you suggest for it?

At the bend of the stomach is the triangular spleen; at the junction of stomach and intestine is the pancreas. Do you find any thin membranes (mesenteries) binding the alimentary tract to the dorsal wall of the celom? Or any similar membrances (omenta) connecting the various

18 LABORATORY WORK.

parts of the tract together? Notice blood-vessels passing from the mid-dorsal line of the ecelom (dorsal aorta) to the intestine (anterior mesenteric artery), to the rectal gland (posterior mesenteric artery), and one more anterior (celie axis) to stomach, liver, and anterior part of intestine.

Draw the alimentary tract as made out, inserting and naming all parts.

Remove the alimentary canal by cutting away most of the liver, the stomach, and the rectum. On the roof of the ccelom are two long ridges either side of the mes- entery. The lateral ones are the ‘kidneys,’ or Wolffian bodies (mesonephros), the much shorter medial ones are the reproductive organs (gonads). Draw this system.

Cut off the skin between the pectoral fins and clean the muscles from the support of the fins (pectoral girdle) which crosses the median line. Is this composed of bone? ~

Cut through the pectoral girdle and lay open the cavity in front of it (pericardial cavity). In this les the heart, consisting of a thick-walled ventricle below, and dorsal to it a thinner-walled auricle. The heart is connected to the posterior wall of the pericardium by a thin-walled sinus venosus. In front of the heart and extending for- ward to the anterior wall of the pericardium is a large blood-vessel, the truncus arteriosus. Sketch the heart, pericardium, etc. (ventral view), and then trace the truncus forward into the flesh in front of the pericardium, cutting carefully. This part is the ventral aorta. Trace from it, right and left, afferent branchial arteries carrying the blood into the partitions between the gill-clefts. Add these vessels and the clefts to the sketch of the heart.

Insert the scissors at the angle of the jaws and cut back- wards along the lower edge of the gill-slits; repeat the operation on the other side and turn back the lower jaw

DOGFISH. 19

and floor of the throat as a flap. This will lay open the cavity of the mouth and the pharynx.

See that the gill-clefts are slits in the wall of the tube, each slit bearing delicate filaments on its walls, while a bar of cartilage (branchial arch) lies in each partition between two successive gill-clefts. See also the internal opening of the spiracle. Is there a bar of cartilage (hyowd arch) between it and the first gill-cleft? Could the spiracle be regarded as a modified gill-cleft? Draw these parts <4.

Slit the skin on the roof of the mouth and carefully remove it with the forceps. This will expose the efferent branchial arteries, which can readily be traced from the septa between the gills to their union to form the dorsal aorta, which runs backward above the