52 



COMPARATIVE ZOOLOGY. 



A great advance is sliown by the Sea-urchin, whose 

 mouth ia provided with five sharp teeth, set in as many 

 jaws, and capable of being projected so as to grasp, as well 

 as to masticate, its food (Figs. 214, SS).. 



In Mollusks having a single shell, as the Snail, the chief 

 organ of prehension is a strap-like tongue, covered witli 

 minute recurved teeth, or spines, with wliieh the animal 



rasps its food, while the upper lip 

 is armed with a sharp, horny 

 plate (Fig. 29). In many marine 

 species, as the Whelk, the tongue 

 is situated at the end of a retrac- 

 tile proboscis, or muscular tube. 

 In the Cuttle-fish, we see the sud- 

 den development of an elaborate 

 system of prehensile organs. Be- 

 sides a spinous tongue, it has a 

 pair of hard mandibles, resem- 

 bling the beak of a Parrot, and 

 working vertically ; and around 

 the mouth are eight or ten pow- 



FiG. 16.-Siickers on the Tentacles p^f,,! arms fnrnishpfl witli nnmpr 



of a cuttie-ii8h ! a, hollow axis of *^""' ^'^"'^ lurnisnea wun numer- 



the arm, coiitiiining nerve and ar- OUS CUp-like SUckcrS. So perfect is 

 tery; c, cellular lissne ; d, radiat- . *■ 



ing fibres; h, raised margin of theadliesioU of tlieSCSUckerS, that 



the disk around the aperture/, (7, . . • j. j. i- i 



which contains a retractile meiii- 't 'S easier tO tear away a iuilb 



brane, or "piston." i. ^,,^^ ^^^ ^^^^.^^j^ j^ ^ ^.^^^ j^^ j^^,^ 



The Earth-worm swallows eartli 

 containing particles of decaying 

 vegetable matter, which it secures 

 with its lips, tlie upper one being 

 prolonged. Otlier worms (as Ne- 

 reis) are so constructed that the 

 gullet, which is frequently armed 



with teeth and forceps, can be p,e. „._i;;.~r:head, with ex- 

 turned inside out, to form a nro- '^""^^^ proboscis.- j,jaw8; t, 



... . i '^ tentacles j H, head ; S, eyes. 



iboscis for seizing prey. 



