. An introduction to zoology, with directions for practical work (invertebrates). 106 INTRODUCTION TO ZOOLOGY. Fifi. 60.—Shell of Limnaea stagnalis, seen from below. s, Spire ; hiv, body wliorl; r, reflected lip of the shell. tion is thick. It is very hardy and can easily be kept in a tank, the only drawback to it being, that it has such an omnivorous and hearty appetite that it is apt to destroy the plants rather too rapidly, and only common weeds should be kept with it. The Canadian water - weed, Anacharis (Elodea) canadensis, which can ^ always be easily obtained, is excellent food for it,
. An introduction to zoology, with directions for practical work (invertebrates). 106 INTRODUCTION TO ZOOLOGY. Fifi. 60.—Shell of Limnaea stagnalis, seen from below. s, Spire ; hiv, body wliorl; r, reflected lip of the shell. tion is thick. It is very hardy and can easily be kept in a tank, the only drawback to it being, that it has such an omnivorous and hearty appetite that it is apt to destroy the plants rather too rapidly, and only common weeds should be kept with it. The Canadian water - weed, Anacharis (Elodea) canadensis, which can ^ always be easily obtained, is excellent food for it, and also the microscopic green algal growths whicb so often cover the sides of a tank. If trained to feed on these, the snail will do valuable work in an aquarium in keeping the glass free from these Algae which obscure the view. The snails should be watched also more detailed observations should be made on a couple of snails kept for a time in a small glass bowl or jar which can be easily handled so that the snail may be seen from all sides. General The soft body is covered by a shell which is Structure, conical in shape, but formed of six or seven spirally The Shell, twisted coils or whorls. The iirst whorl is so small as to be a mere dot, but each successive whorl is larger, and is in close contact with the whorl before. The seventh or last whorl is bigger than all the others put together, and this is called the hody whmi, all the rest of the shell forming the spire; the free edge of the body whorl is known as the lip. If the shell is viewed from a point vertically above the apex of the spire, the whorls are seen to descend in a right- handed spiral; hence it is termed "; (When the spiral turns to the left a shell is called " ;) On the body whorl many delicate lines can be seen parallel to the lip, and at intervals a few more deeply marked lines occur. These are due to its discontinuous method of growth. It is frequently added to at it
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