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 w T ell 
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- 
’1“: erful arms furnished with numer- 
the arm, containing nerve and ar- 0 US CUD-like SUCkerS. So perfect is 
tery; c, cellular tissue; d, radiat- * t 
ing fibres; h, raised margin of the adhesion of these suckers, that 
the disk around the aperture/, g, ... . . 
which contains a retractile mem- it is easier to tear away a limb 
brane, or “piston," u than ft from its hold. 
The Earth-worm swallows earthy 
matter and decaying leaves, which 
it secures with its lips, the up¬ 
per one being prolonged. Other 
worms (as Nereis) are so construct¬ 
ed that the gullet, which is fre¬ 
quently armed with teeth and for¬ 
ceps, Can be turned inside out, to Fig.it.—N ereis — head, with ex- 
form a proboscis for seizing prey. y ' 
