GASTEROPODS. 
7 
ranged on long arms, while those of the Lamelli- 
branehs are in plates or folds, resembling in ap- 
pearance a line 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-gilled 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 world 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 caught by the mucous on the gills, 
rolled into threads, and canied to the mouth, 
thus furnishing the animal with its food. 
The Gasteropods which live in vrater likewise 
have gills to purify their blood, but move around 
in search of their food, w T hich 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. 
