GASTEROPODS. 



ranged on long arms, while those of the Lamelli- 

 branchs are in plates or folds, resembling in ap- 

 pearance a fine toothed comb. In this little book 

 we shall speak of only the second and last classes, 

 the other being less numerous on the sea-shore, and 

 of less importance to the student. 



The Gasteropods are more highly organized 

 than their plate-billed neighbors, and most of 

 them rejoice in that chief emblem of dignity, a 

 head. Lamellibranchs, on the other hand, being 

 destitute of that appendage, are known as aceph- 

 als, or headless animals. The acephals do not 

 get their food by eating, but rather by breathing. 

 Most of them live buried in the mud and com- 

 municate with the outside w T orld by means of two 

 pipes or siphons. Through one of these tubes 

 they pump in water from above, then pass it over 

 their gills, and expel it through the other siphon. 

 The water, in passing over the long plate-gills, 

 supplies both air and food ; first, the dissolved ox- 

 ygen which it contains purifies the blood of the 

 animal, and secondly, the great numbers of min- 

 ute animal and vegetable forms contained in the 

 water are caujrht by the mucous on the gills, 

 rolled into threads, and carried to the mouth, 

 thus furnishing the animal with its food. 



The Gasteropods which live in water likewise 

 have gills to purify their blood, but move around 

 in search of their food, which they gather by 

 means of a rasp-like tongue. Some of them feed 

 on sea-weeds and other marine vegetables, while 

 others are scavengers, clearing the sea of dead 

 fish and the like. Not a few are predaceous, and 

 do not scruple to attack living animals, especially 

 the more helpless kinds of mollusks. 



