. Animal forms; a second book of zoology. Zoology. Si ANIMAL FORMS masticatory apparatus which consists of a kind of tongue with eight to forty thousand minute teeth in our land forms (Fig. 51), while in certain marine snails they are beyond computation. With the licking motion of the tongue this rasp tears the food into shreds before it is swallowed, and in the whelks or borers it serves to wear a circular hole through the shells of other mollusks, which are thus killed and devoured. This latter process is facili- tated by the secretion of the salivary glands, which has a softening effect upo
. Animal forms; a second book of zoology. Zoology. Si ANIMAL FORMS masticatory apparatus which consists of a kind of tongue with eight to forty thousand minute teeth in our land forms (Fig. 51), while in certain marine snails they are beyond computation. With the licking motion of the tongue this rasp tears the food into shreds before it is swallowed, and in the whelks or borers it serves to wear a circular hole through the shells of other mollusks, which are thus killed and devoured. This latter process is facili- tated by the secretion of the salivary glands, which has a softening effect upon the shell. Ordinarily the saliva o\ snails exercises some di- gestive Kit;. 51.—A small portion o( the radula or tongue rasp of a snail (SyCOtypilS). In the stomach of some snails are teeth or horny ridges which also are instrumental in crushing the food, and in numerous minor respects peculiarities exist in differ- ed species according to the nature of the food; but in its general features the digestive tract is similar to that of the clams. The processes of circulation and excretion are also car- ried on by means of systems which show a certain resem- blance to those o\' the clams. As might be expected, certain differences exist, sometimes very great, but they are of too technical a nature to concern us further, 85. Sense-organs of lamellibranchs and gasteropods.— The eyes of mollusks differ widely in their structure and the position they occupy in the body. In our common land snails two pairs of tentacles are borne on the head, the lower acting as feelers, while each of the upper ones bears on its extremity the eye, appearing as a minute black dot (Fig. IS). In this same position the eyes of many marine snails occur, but there are numerous species in which there are other accessory eyes. In many of the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these
Size: 1898px × 1316px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
