First book of zoölogy

Front matter

RNew Dork State College of Agriculture

At Cornell Aniversitp Bthaca, N. PB.

First book of zoolog

CHAPTER I. PAGE FRESH-WATER SHELLS . ‘ 3 F , a

Where to collect, 1; Empty or Dead Shells, 2; Parts of a Shell named, 3; Forms of Spire, Dextral, and Sinistral Shells, 4; Lines of Growth, Growth of a Shell, 5, 6.

CHAPTER IL Fresh-wATer SNAILS 4 - : . 3 Pog

Where and how to collect, 7,8; Live Shells, 8; Head, Tentacles, Foot, how they breathe, 9,10; Operculum, 12; Gills, 18.

CHAPTER III. Lanp Sars é ; F : é . 14

Where to collect, 14; Parts of the Animal, 15,16; Tentacles, Jaw, 17; Explanation about an Object being enlarged, 18; Slug, 19; Eggs and Young, 20; Mantle, 21.

CHAPTER IV. Sea SNAILS. ‘ , é ‘ « 21

Where to collect, 22; Entire Aperture, Aperture Notched or Canaliculated, 23; Siee and its Uses, 24; Flesh and Animal Feeders, 25; Egg-cases or Capsules,

Chapter V

Where found, 27; Ligament, Lines of Growth, 28; Regions of Mussel, 29; How they crawl, 30; Excurrent and Incurrent Orifices, 31; Siphons, Mantle, 32; How Pearls are formed, 33; Internal Markings of Shell, Hinge, 34; How the Shells open and Ligament acts, 36.

x CONTENTS.

CHAPTER VI. Ciams, MussELs, AND OYSTERS : ‘ ‘

Salt-water Bivalves, 37; Parts of a Clam, Siphons, Currents of Water, and how they eat, 3s, 39; Ligament, and Internal Markings of Shell, 40; Byssus, 42; Siphonal Tubes separate, 44; Oysters, 45; Heart, Palpi, Liver, Gills, Mouth of Oyster, 46, 47; Relations between Clams, Musxcls, and Snails, 48,

Chapter X

Growts or Insects Collecting Eggs, Caterpillars, Chrysalides, 71, 72; Where to collect, 73; Eggs, 74; Raising Caterpillars, 15, 77; Chrysalis, 7x. 79; Development of Chrysalis, £0;

Incomplete Changes, 81; Complete and Incomplete Metamorphosis, $Y ; Difference between Larva and True Worms, §3-50.

CHAPTER XI. Hapits anp Structure or Ixsecrs ‘ ‘ P

Mud-wasp, S5-87; Mosquito, 83.

CHAPTER XII. Hapits anp Structure or Insects (continued) : P

Young Grasshopper, 89; Cast-off Skin of Grasshopper, 90; Curious Accidents, 91: Air-tubes, 92; How'Insects breathe, and how some rest, 93; Sounds produced by Insects, 94; Stridulation of Grasshopper, 95, 96.

PAGE

"1

CONTENTS. i

Chapter XIII

PAGE Hasits anp Srructure or Insects (continued) . ‘ . . 97 Spittle Insect, 97, 98; Cicada or Seventeen-year Locust, 99, 100. CHAPTER XIV.

Hasits anp Srrucroure or Insects (concluded) . : ji . 101 May Fly or Ephemera, 100-103; Caddis Worm, 104; Gall Fly, 104, 105; Other Galls, 106.

Chapter XV

SPIDERS : ‘ . 2 ji ‘ . 109 Parts of a Spider, 110; Mouth Parts and Eyes, 111; Spinnerets, 112; Legs, 113; Habits of some, 114; Net Building, 115; Ballooning Spiders, 116, 117; Egg Cases, Young Spiders, 117, 118, Care for the Youn,, 119, 120. CHAPTER XVI.

DappyY-LONG-LEGS, CENTIPEDES, AND MILLIPEDES : : é . 121 Daddy-long-legs, 121-123 ; Centipedes, 128, 124; Mouth, Parts of, 125; Millepedes, 126 ; How they lay their Eggs, and Young, 127; Comparison between Myrioneue and Insects, 127, 128; Some Characters of Insects, Spiders, and Myriopods, CHAPTER XVII.

Craw-Fish anp Lopster . és . : . 180 Craw-Fish, where found, 130; Regions of, 131; Mouth Parts and Appendages, 132, 133; Gills, 184; How to arrange Parts, 135, 186; Moulting, 187; Young Lobster, 188.

CHAPTER XVIII.

Crass, Hermit-Crabs, AND OTHER CRUSTACEANS ‘ P é . 188 Common Crab, 189; Eggs, and how they carry them, 140; Fin-like Legs, Oyster Crab, 141; Hermit Crab, 142-144; Fresh-water Crustaceans, 144; Sowbug and Eggs, 145, 146; Regions of Crustacea, 146, 147.

CHAPTER XIX.

BivaLVE CRUSTACEANS AND BaRNACLES . 147

Characters of, 148, 149; Where found, 150; Appendages, how they secure their Food, 151; Young Barnacles, 152, 153. :

xii CONTENTS.

CHAPTER XX.

Worms i “ ‘i : F .

Angle Worms, 154; How they move, 154, 155; Leech, 155; Sea-Worms, 156, 157; Tube-building Worms, 159

CHAPTER XXI.

ConcERNING NATURAL Groups

Characters of Articulates, 160; Of Wormsand Mollusks, 161 ; Type Characters, 161 ; Typical Animals, 162 ; Systematic Tables and Classification, 163.

CHAPTER XXII.

CHARACTERS OF VERTEBRATES External Characters of Salamanders, 168, 164; Comparison with Cat, 165; Differences between the two, 166; Young Salamander, 166; Skeleton of Cat, 167;

Vertebral Column and Spinal Cord, 169, 170; Bones of the Ankle and Wrist, 171, 172; Groups of Vertebrates, 178, 174.

CHAPTER XXIII.

Bones or tue Lea ann Wixe or Birps Importance of studying Young Forms, 174; Wing Bones of an Adult Bird, 175;

Embryo Birds, and Wing Bones of same, 176; Leg Bones of an Adult Bird, 177; Leg Bones of Embryo Bird, 178; Leg Bones of Young Toad, 180.

CHAPTER XXIV.

CLasses AnD Sus-Kinepoms ‘

Sub-Kingdom Mollusca, Class Gasteropoda, 151; Class Acephala, 182; Sub-Kingdom Arthropoda, Class Insecta, 183; Class Myriopoda, 184; Class Arachnida, 185; Sub-Kingdom Vermes, Class Annelida, 155; Class Crustacea, 156; Sub- Kingdom Vertebrata, 187. :

Notice to Teachers a ‘ s

PAGE . 158

. 160

FIRST BOOK OF ZOOLOGY.

Chapter I. Fresh-water Shells

For these lessons, it has been deemed best to commence with the shells of mollusks, such as snail-shells and mussels. They are better objects to examine than insects, being more simple in structure, and less liable to be broken in handling. When found alive, their habits can be readily studied, as they can easily be kept alive in jars filled with water.

1. Let the pupils first make a collection along the shores of some lake or river, picking up all the different kinds of shells they meet with. The waves will have thrown them up on the shores, or in times of drought the waters will have left them exposed. Certain kinds are very small, though they will be found by sharp looking. Most of the shells collected will be empty, and these shells are called dead shells, because the soft-bodied creatures once contained in them have died and decayed, leaving the hard, limy shells. Some of the shells collected may contain the animal, and at one time all of them possessed a little creature within, which was the fabricator of the shell.

2. Remember that the shell is not a house built by the snail, as a wasp builds its nest, but the shell isa part of the animal, and is connected to it by certain muscles, so that it cannot leave the shell, as many suppose.

The empty, or dead, shells, are to be studied first.

Looking over the shells collected, we shall find some of the following kinds :

Fig. 1.—Fresa-Water SHELLS.

A number of fresh-water mussel-shells, also, will probably be collected.

Fig, 2,—Fresa-Water MusseL-SHELL.

These are to be reserved for future examination. Those

FRESH-WATER SHELLS. 3 having a spiral turn or twist are called snail shells, and are to be studied first.

3. Let the pupils pick out from their collections the shells like these :

Fic. 8.—Fresu-W ater §nait-SHEL.s.

The different spiral turns, or twists, are called whorls, and the whorls together form the spire. The opening into the shell is called the aperture, and the line separating the whorls is called the suture. The pointed end of the spire is called the apew.

whorls forming the spire.

aperture,

Fic. 4.—SHELL, WITH Parts NAMED.

In some shells the spire is elongated ; in others the spire is short ; in others still the spire is depressed or flattened.

Fie. 5. {\ = @)y XI G) SPIRE ELONGATED. Suort. FLATTENED.

4. If the shell is held in the hand, with the aperture toward the holder, and the spire pointing upward, as in the figures drawn, the aperture will be either toward the right hand, or toward the left hand. In the figures already given, the aperture is on the right hand, and these shells are called dextral, or right-handed, shells.

Shells having the aperture on the left hand when held in the way above described, are called sndstral, or left-handed, shells. Let the pupils here examine all the shells they have collected, holding each one with the spire pointing upward, and the aperture toward them, and separate the dextral shells from the sinistral shells. As sinistral shells are not as common as the other kind, it may be that none will be found in the first collections made by the pupils. The following is a figure of a sinistral shell :

Fie. 6.—SinistraL SHELL.

FRESH-WATER SHELLS. 5

5. If the surface of the shell be examined closely, delicate lines running from one suture to another will be seen, as in the figures already given ; and, if the shell be looked at from the side of the aperture, these lines will be found running parallel to the edge of the aperture, or lip, as it is called.

These delicate lines are called lines of growth.

Iie. 7.—Suowrne Linrs or GROWTH RUNNING PARALLEL TO THE EDGE OF THE APERTURE.

The shell is increased in size by successive layers of shelly matter added to the borders of the aperture. In this way the shell grows.

A clearer idea of the growth of a shell may be obtained by studying the next figure (Fig. 8): A representing in outline a young shell; & representing the full-grown shell in outline; and Crepresenting the same outline as B, with a number of lines of growth represented upon it.

If the shell were now to continue its growth a single halfturn, or whorl, the dotted lines would indicate the increased stages it would assume: @ representing the first increase in size, 6 the next stage, and ¢ the appearance of the shell when the additional half-whorl has been completed.

c b Fra. 8.—ILLUSTRATING THE INCREASE IN S1zE OF A SHELL.

Among the lot of shells collected by the pupil, differentsized ones will be found. Now, if a number of these, of different sizes, can be picked out, provided they belong to the same kind, or species, it will be noticed that the apex of all of them will be the same; but that the shells have increased in size at the aperture, and the aperture will be larger, and the larger shells will have more whorls than the smaller shells. The following figures illustrate four different ages of the same species of shell :

Fig. 9.—ILLustRATING DIFFERENT AGES OF THE SAME SHELL—THE LOWER FIGURES REPRE- SENTING A VIEW OF TIF SUELL FROM THE APEX.

6. The axis around which the whorls revolve is called the columella. This axis is generally solid, though in many shells it is hollow, as if the whorls had turned around a shaft which had afterward been withdrawn. This hollow axis looks like an opening in the base of the shell, as in the following figure :

Fie. 10.—A SNaATL-SHELL SEEN FROM BELOW.

This opening is called the wmbilicus. The apex of the shell is sometimes called the nucleus, because the shell commences to grow from this point.

Chapter II. Fresh-water Snails

7. Tue pupils will now be required to bring in some live snails. Let them examine bits of bark, chips, or branches, found in ditches, or muddy brooks. Under lily-pads and on the stems and leaves of other aquatic plants, and on stones in rivers, snails of various kinds will be found. A dipper with the bottom perforated, or made into a sieve, and attached to a wooden handle four or five feet in length, will be found useful in scooping up the sand or mud from the bottom of rivers and ditches. The dirt having been sifted out, the shells and other objects will be left behind. The dipper may be made as in the figure.

os

Fic. 11.—Dipprr ATTACHED TO A Wooprn HanDLE FOR COLLECTING SNAILS.

Shells collected with the snails inside, and cleaned for the cabinet, are called (ive shells. They are always more fresh and perfect than dead shells.

Having made the collection, the snails should be kept alive in a wide-mouthed jar, or bottle, care being taken not to have more than fifteen or twenty in a jar holding a quart of water.

8. The pupils will have secured some of the following forms:

The broad, creeping disk upon which the snail rests, and by which it retains its hold to the glass, is called the fvot. The snail moves about, and crawls or glides slowly along, by means of the foot.

The two little horns or feelers, in front, are called tentacles, and, as the snail moves, the tentacles are seen stretched out in front, and occasionally bending, as if the creature were feeling its way along. The eyes are seen at the base of the tentacles, as two minute black dots. The mouth is between the tentacles, and below. The part from which the tentacles spring is called the head, and the opposite end of the body is called the ¢add. The surface upon which the snail rests is called the ventral or lower surface, and consequently that portion of the body which is above is called the dorsal surface, or back.

9. The pupil, in watching the habits of the snails he has collected, will notice some of them crawling to the surface of the water to breathe air. The snail accomplishes this by raising the outer edge of the aperture to the water’s edge, and then opening a little orifice in the side, through which the air enters to the simple lung within.

This orifice is on the right side in those snails having dextral shells, and on the left side in those snails having sinistral shells.

Many kinds of snails which live in fresh water are called air-breathers, because they are forced to come to the surface of the water to breathe air. In doing so they first expel a bubble of air, which may be seen escaping from the breathing-orifice, as in Fig. 14, B.

A view from the back, or dorsal view.

side-view.

ventral view. zt. Tentacles. e¢, Eyes. 0, Breathing-orifice. m, Mouth.

Fic. 183—A Fresn-Water SNAtL 6EEN FROM ABOVE, FROM THE SIDE, AND FROM BELOW.

These fresh-water air-breathing snails may be kept under water for many hours before life is extinct.

Fra. 14.—Jar of water, in which is contained a number of species of mollusks, some of which have already been studied. Some of them are near the surface, breathing air: A and C are taking in air; Bis just expelling a bubble of air from the lung; D is crawling on the surface of the water; Z, G, and J, are in the act of crawling up, to get a fresh supply of air; and Jis a water-breather, having gills, but no lung.

10. Among the snails collected, there will probably be found some which have a peculiar scale on the hinder part of the body. When the snail crawls, this scale will be seen just behind the shell, as in Fig. 15, 0

This scale is called the operculum, and when the snail has contracted, or drawn within the shell, the operculum is seen to fit the aperture of the shell, closing the shell asa stopper closes the mouth of a bottle.

Fie. 15.—Snan. wir OPpERCULUM.—o0, a e, Eye; 7, Rostrum; g, Entrance to Gillavity.

Nearly all sea-snails, that is, snails which live in salt-water, and many species of fresh-water snails, and also many snails which live in damp places on the land, and which are called land snails, have an operculum.

When the snail has retired within the shell, the operculum will look like this in the aperture of the shell (Fig. 16):

A series of concentric lines will be seen marking the operculum, and these are the lines of growth, the operculum growing around the outer edge by successive additions, just as the shell grows by successive additions to its outer inargin.

The Western rivers teem with species of snails having opercula. 11. If the pupil has any of these operculated snails alive,

Fic, 16.—APERTURE OF SHELL CLOSED BY OPERCULUN, 0.

he will observe that they do not come to the surface to breathe air.

Instead of a lung, they have a cavity containing an organ, or part, called the gill, by means of which the snail is capable of getting from the water what the air-breathing snail gets from the air, namely, oxygen.’

It will be seen that the head of the snail is shaped differently in the snails having an operculum, the mouth being at the end of a sort of proboscis or rostrum. (See Fig. 15.) The shells, too, are, as a general thing, more solid.

12. Thus far the pupils have examined those snails which live in fresh water. Some of these were air-breathers, and came to the surface of the water at intervals to breathe air. He has studied other fresh-water snails which did not breathe air directly, but performed this function by means of

1If the class is sufficiently advanced, the teacher may here explain about oxygen and what the blood requires, and gets by respiration.

an organ called the gill. And these snails were operculated, that is, they all possessed a little scale called the operculum, which closed the aperture tightly when the snail contracted within the shell.

He has also learned that the shells grow in size by successive additions of limy matter deposited around the free border of the aperture, and that the delicate lines which mark the surface of the shell, and which run parallel to the outer edge of the aperture, are lines of accretion, or lines of growth.

Chapter III. Land Snails

13. Turrr are many other species of snails which live out of the water altogether, though they are generally found in damp places; and these are called land snails, because they live on the land.

Let the pupils now endeavor to collect some land snails. By going to some hard-wood grove of maple, beech, or oak, and turning over the layers of dead leaves, old rotten logs, or pieces of bark, they will be sure to find some specimens of land snails. Some of them do not grow larger than a pin’s-head, others have shells as large as a walnut.

They are generally light brown in color, and the smaller species often have highly-polished or shiny shells.

The spire is generally depressed or flattened. In many,

LAND SNAILS. 15 the border of the aperture has a thickened white rim, or lip, as it is called. Such a collection having been made, the pupil will find among them some of the following kinds:

Fig. 17.—Tur SHetis or Lanp Swarts,

14. The snail, as it crawls along, leaves a slimy trail after it. This trail consists of a fluid, which not only flows from the creeping disk, but also from the surface of the body. If the back of the snail is irritated by a sharppointed stick, a little whitish mass of this fluid, or mucus, will adhere to the end of the stick.

By placing the snail on a piece of glass, and allowing it to adhere and crawl on it, a good view may be obtained of the peculiar movements of this creeping disk, by looking through the glass from the other side.

The breathing-orifice may be found just within the aperture of the shell, on the right side of the snail.

This orifice will be seen opening and closing at intervals. (See Fig. 18, 5.)

15. In the fresh-water snails there are but two tentacles upon the head. In the land snails with few exceptions, the x tentacles are four in number, a larger and a smaller pair. The larger tentacles are called the superior tentacles ; the

Fig. 18—LanpD-SNaILs CRAWLING.—0, Breathing Orifice; s ¢, Superior Tentacles; ¢ ¢, Inferior Tentacles; m, Mouth.

smaller ones, often appearing as mere tubercles, are called the inferior tentacles. (See Fig. 18, s¢and 77%.) As the snail crawls, the superior tentacles are seen in constant motion, as if the creature were feeling its way about with them.

The eyes, instead of being at the base of the tentacles, as in the fresh-water snails, are found at the tip of the superior tentacles.

In the land snails, with few exceptions, the tentacles can be drawn within the head, and for this reason they are also called retractile tentacles.

While the snail is crawling, let the pupil touch the end of the tentacle with his finger, or, even if he alarm the snail by a sudden jar, he will see the tentacles quickly withdraw within the head. The pupil will observe that the bulbous

LAND SNAILS. 1"

end containing the eye disappears first, as the end of a glovefinger disappears, when the hand is withdrawn from the glove, the glove turning wrong-side out.

al Fic. 19.—SnHowine SNAIL WITH TENTACLES RETRACTED, A; AND TENTACLES PROTRUDED, B.

16. Something may now be learned as to the way in which land snails eat.

By placing before the snail the tender leaves of lettuce or cabbage, the head will be seen to move, as little mouthfuls of the leaf are bitten off. The upper lip of the mouth is furnished with a hardened piece called the buccal plate. It is crescentic in shape, and, in some species, the cutting edge is notched, so that it acts like an upper set of teeth, by which it bites off little bits of the leaf. The floor of the mouth is lined by a membrane having upon it rows of little points which enable the snail to rasp and grind its food. These parts

Fic. 20.—Jaw, on Buccan Prats or a LAnp SNAIL, HIGHLY MAGNIFIED.—{It can just be discerned without a microscope.)

are so minute that they can be studied only by the aid of a microscope. If the pupil will watch his fresh-water snail as it crawls around the sides of the jar, he will see at intervals the mouth open, and a glistening tongue appear, as the snail laps up the scum which forms upon the surface of the glass.

Nore ror Teacuers anp Pupiis.—Let the teacher here explain to the pupils what is meant by an object being magnified.

If the teacher has a common magnifying-glass, let each pupil in turn observe its magnifying effect, by looking at a common house-fly, or the printed page of a book. Ifa microscope can be shown the class, it will be better still.

Let it be explained, also, what is meant by an object being enlarged two, or three, or more times. To be enlarged two or three times, is to make the object two or three times as long as it was before, and of proportional bigness.

Oftentimes the object has to be reduced in size in the figure, as in pictures of large animals, in the picture of an elephant, for example.

In representations of very small animals, however, the figure has to be enlarged in order to show parts plainly that could not otherwise be seen, were they drawn natural size, that is, a size corresponding to the actual size of the animal.

Thus in Fig. 24, 6 and ¢ are greatly enlarged, to show the little snail within the egg:

17. In searching for snails, the pupil will come across snail-like animals, which.have no coiled shells on their backs. Let the pupil examine the under side of damp boards or plank walks in gardens, and he will be sure to find them.

They are very common in old gardens in cities. These

Fig, 21.--A SLUG CONTRACTED.

creatures will be found clinging to the board or upon the ground, and will present this appearance (Tig. 21). Soon, however, they will stretch out their tentacles, and commence

LAND SNAILS. 19 to crawl, and then their resemblance to the shell-bearing snails will be seen at once.

Instead of having a coiled shell into which they can retreat when alarmed, they have a little limy scale imbedded in a portion of the back, called the mantle. The breathing-orifice is on the right side of the body, and the tentacles, mouth-parts, creeping disk, and other features, are quite similar to the land snails already studied.

Fie, 22.—A Naxep Lanp SNAIL, or SLUG, FULLY EXPANDED.—«, Mantle; 6, Breathing- Orifice.

18. On the approach of winter, land snails bury themselves in the ground, and those that have shells retire within the shell as far as possible, and close the aperture of the shell with a film of the mucus which the body secretes so abundantly. In this condition they remain dormant until the warm weather of spring revives them again.

If the pupil will collect a lot of snails in the early spring, and keep them confined in a box, with earth, damp leaves, or bits of rotten wood or bark, the snails in the course of a few weeks will lay a number of little eggs. These eggs will be white and round, about the size of a pin’s-head. By careful tending, that is, by keeping the leaves slightly moist, the eggs will hatch out tiny snails, and these will attain half their mature size the first season.

Fie. 28.—a, Eggs of Land Snail; 6, Young Snail just hatched; c, Young Snail somewhat advanced: b and ¢ are magnified.

19. If the pupil will also collect a lot of fresh-water air-breathing snails, and keep them alive, they will deposit their eges upon the sides of the glass jar in which they are confined. These eggs will be oval in shape, and transparent, and will be inclosed in a transparent, jelly-like substance. Tig. 14, ZH, represents the appearance of a cluster of these eggs.

Fig. 24 shows a cluster of eggs with the appearance of two eggs highly magnified, showing the young snails as they appear within the egg.

Fic. 24.—a, Cluster of Eggs of a Fresh-Water Snail; 0, c, Eggs enlarged, showing the + young Snails within the Eggs.

With the aid of a magnifying-glass, the eggs may be watched from day to day, aud the young snail can be seen in its various stages of growth.

LAND SNAILS. 21

20. If a land-snail is taken out of its shell (and this can be done if boiling water be first poured upon it, and then with a pin the animal can be readily picked out), it will present this appearance (Fig. 25) :

Fie. 25,—Lanp guar REMOVED FROM ITs SHELL. —m, Mantle.

The portion contained within the shell presents the same general appearance as the shell itself. A free border, or collar, is seen which corresponds to the aperture of the shell. This border is called the mantle, and is a characteristic feature of all the snails thus far studied. It is the edge of the mantle which deposits the successive layers of the shell, and increases its size. In the slug, there is only the limy scale; this is buried in the mantle, which is plainly seen covering a portion of the back, like a shield (Fig. 22, a).

Chapter IV. Sea Snails

91. Crasszs that live near the sea-coast may now study the marine, or salt-water snails. These may be collected alive at low tide, upon rocks, or under the sea-weed. By examining pools left at low tide, many little sea snails may be seen creeping about.

A good place to collect dead shells may be found along an exposed beach. After a violent storm, when the waves have been running high, a great many animals are thrown up from the sea, and among them many shells may be secured.

The following will be some of the shells collected :

Fig. 26.—Comumon Sra Snams,

22. With very few exceptions, all sea snails are waterbreathers; that is, they are furnished with gills, instead of a simple lung. Most of them are operculated.

In the shells collected the pupil will find two well-marked groups.

In the two lower right-hand figures of Fig. 26, the shells have an aperture with a continuous border; that is,

SEA SNAILS. 93 there is no notch, or fold, in it. In the three upper figures there is a notch, or fold, in the base of the aperture.

This notch is called the canal, and in some species it is very short, while in other species it is very long, as in Fig. 27.

The mantle of the animal is prolonged in a fold which occupies this canal, and is called the siphon. Through this fold or siphon the water finds access to the gills. (Fig. 28 shows another species. The siphon is seen as a fold of the mantle running into the canal of the shell.)

23. A very common species, found in the greatest abundance from Maine to Florida, on mud-flats, will give a good illustration of the uses of the siphon. In this particular species, the siphon is much longer than the canal, and, when the snail is crawling, the siphon is bent upward. <As the

Fig. 28.—A Sra SNAIL SEEN FROM BELOW.—é, Eye; m, Mouth; , Siphon.

habit of this species is to crawl along partly buried in the mud, the siphon, projecting above the level of the mud, conducts the pure sea-water to the gills of the snail below. Fig. 29 illustrates the appearance of this snail :

Fra. 29,—A, the Snail crawling upon the Surface of the Mud; B, the same slightly buried; CG, the same nearly buried; the Siphon, s, id seen curved upward.

SEA SNAILS. 25

Such shells are called canaliculated shells.

The aperture of the shell is said to be entire, when it does not possess this notch, or canal. Let the pupil separate the shells having the aperture entire, from those shells haying a canal.

These differences in the shell, as slight as they appear, are accompanied by corresponding differences in the character and habits of the animal.

Those snails having the aperture of the shell entire are with few exceptions vegetable-feeders, while those having a canal to the shell are flesh-feeders. The mouth-parts, and opercula, too, are different in the two groups.

24, Other shells will be found differing greatly in appearance from those thus far studied. One of these is represented in the lower left-hand corner of Fig. 26.

Another species, called the limpet, looks like this (Fig. 30):

Fig. 30.—SHeit or Lovrer.

These shells will be found sticking with great tenacity to the rocks, and some skill and force will be required to remove them. This can be done by using the large blade of a pocket-knife, and suddenly scraping them from the rock. If they are then placed in a saucer of water, with the shell downward, the animal within will be found to have the broad, creeping disk, head, tentacles, and other parts, peculiar to the snails already studied.