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 mouth are eight or ten pow- 
Fig. 16.-Suckers on the Tentacles er f u ] arms furnished with I HI 171 Gl*- 
of a Cuttle-fish : a, hollow axis of 
the arm, containing nerve and ar- QilS Clip-like SUckerS. So perfect is 
tery; c, cellular tissue; d, radiat- . . . 
ing fibres; h, raised margin of tile ad hesion ot these SUCKei'S, that 
the di^k around the aperture/, q, ... • , , i • -t 
which contains a retractile mem- ^ easier to tear away a limb 
brane, or “piston,” i. than to detach it f 1*0171 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 FiG.n.-Nereis-head, with ex- 
turned inside out, to form a pro 
boscis for seizing prey. 
tended proboscis: J, jaws; T t 
tentacles; II, head ; E, eyes. 
