296 



THE INHABITANTS OF THE SEA. 



Tentacles and eye ot Murex. 

 c. Eye highly magnified. 



humble sphere of existence. The organs of sight are generally 



situated either on a promi- 

 nence at the base of the 

 superior pair of tentacles 

 or, as, for instance, in the 

 Murex, at the extremity 

 of these organs (a, b), a 

 position which enables 

 the animal to direct them 

 readily to different ob- 

 jects. 



Many of the Grasteropods 

 are evidently capable of 

 perceiving odours ; thus, 

 animal substances let down 

 in a net to the bottom will 

 attract thousands of Nassae 

 in one night. We also may 

 infer that they are not de- 

 ficient in taste from the presence of papillae at the bottom of 

 their mouth, analogous to those found on the tongue of other 

 animals ; but, of all their senses, that of touch is undoubtedly 

 the most perfect. The whole soft surface of the body is indeed 

 of exquisite sensibility, but more especially the vascular foot, 

 and the tentacles, or horns, which vary both in number and in 

 shape in different genera. Yet, in spite of this delicacy in 

 the organisation of the skin, which makes it so sensible of 

 contact, it appears to have been beneficently ordered that 

 animals so helpless and exposed to injury from every quarter 

 are but little sensible to pain. Although they are deprived of 

 all higher instincts, we find among the Grasteropods a few 

 examples of concealment under extraneous objects, which 

 remind us of the masks and artifices frequently employed by 

 the insects and crustaceans. 



The Agglutinating Top {Trochus agglutinins) covers itself 

 with small stones and fragments of shells, and thus shielded 

 from the view escapes the voracity of many an enemy but 

 little suspecting the savoury morsel hidden under the mound of 

 rubbish which he disdainfully passes by. 



In animals which are only provided with passive means of 



