CHAP. IV. MOTIONS OP SNAILS AND REPTILES. 9^ 



it not only digs into the sand, but is likewise enabled, 

 by the great power of inflection which is vested in 

 this instrument, to draw the glutinous matter which 

 proceeds from it into threads, and thus to secure itself 

 in its position. * 



(116.) Among univalves, the Helices, or snails 

 and slugs, have a different mode of progression ; the 

 disk of the belly, the sides of which are often di- 

 lated, compensates for the absence of feet, and enables 

 the animal to glide along in the way that almost every 

 one has witnessed ; while the glutinous slime which is 

 emitted by its body, enables it to adhere firmly to even 

 the smoothest surfaces. The Cephalopoda, or cuttlefish 

 tribe {fig. 25.), are supplied with 

 25 ^ ]) /f\ numerous arms, all liberally fur- 

 nished with cups, or suckers ; and 

 by these they seize their prey, 

 perform the most important 

 movements, and attach them- 

 selves to rocks with such a strong 

 adhesion, that it is often more 

 easy to tear off the arms, than 

 to separate them from the sub- 

 stance to which they are affixed. 

 Many are furnished with two 

 triangular fins, one on each side 

 the body, which give them the 

 power of passing as rapidly 

 through the water as ordinary 

 fishes. There is reason to sup- 

 pose that the arms above al- 

 luded to likewise perform the 

 office of feet, by which means 

 these singular animals can crawl 

 at the bottom of the sea : hence 



the scientific name they have acquired of Cephalopoda, 

 signifying a head surrounded with feet. These, the 

 Pteropoda, and Heteropoda, are the only Mollusca, tes- 



* Anira. Biog. vol. iU. p. 450. 



