52 



COMPARATIVE ZOOLOGY. 



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

 mouth is 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, 28). 



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

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

 minute recurved teeth, or spines, with which 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 rnouth are eight or ten pow- 



FIG ^.-Suckers on the Tentacles erf ul armg f urn j s h e d With numer- 

 of a Cuttle-fish : a, hollow axis of 



the arm, containing nerve and ar- QUS Clip-like SUCkerS. So perfect IB 

 tery; c, cellular tissue; d, radiat- . 



ing fibres; h, raised margin of the adhesion OT these SUCKCrS, that 



T^" TO &QQ"1OY ^ f\ 'f'OQY* QXI7QV Q 1 1 TY1 rfc 



which coiit'iins *i rctnctilG in 6 ID- ^^ t?ci&iv>i \j\j Lt/tii dwcty ci> IIIHL* 



brane, or "piston," I. tnan fo d e t ac h it from its hold. 



The Earth-worm swallows earth 

 containing particles of decaying 

 vegetable matter, which it secures 

 with its lips, the upper one being 

 prolonged. Other worms (as Ne- 

 reis) are so constructed that the 

 gullet, which is frequently armed 

 with teeth and forceps, can be 

 turned inside out, to form a pro- 

 boscis for seizing prey. 



FIG. 17. Nereis head, with ex- 

 tended proboscis: J, jaws ; T, 

 tentacles ; //, head ; E, eyes. 



