MOLLUSC A. gy 



last (Fig. 28, Eolis), though more or less protected in 

 the others. Notwithstanding this fact, they have a shell 

 and an operculum in the young, as have all others. 

 Fig. 31 is the young of Dota coronata, which moves 

 freely about by means of the ciliated lobes {vet) ; has 

 a foot (F), which secretes the operculum {opr), eyes, 

 and a mouth, with an oval shell {apx) below, into 

 which it can be withdrawn when alarmed. 



It must not be imagined that I have attempted to 

 give any adequate idea of the different forms of the 

 Mollusca. The foot, for example, may be almost oblit- 

 erated in some forms, and in others suffer the most 

 extraordinary modifications, fitting parts of it to be, not 

 only the ordinary walking apparatus here described, 

 but a swimming organ (Fig. -^Z, 39)? a climbing and 

 leaping organ (Fig. 40), and so on, sometimes spHt 

 longitudinally, sometimes transversely, som'etimes a 

 mere lump or plug, and in other cases reduced to a 

 secreting gland. 



CEPHALOPODS. 



The principal forms of this class of the Mollusca can 

 barely be mentioned, though the author feels that this 

 omission is the sacrifice of an opportunity, which may 

 never recur, of putting before teachers the results of 

 special researches upon one of the most intensely inter- 

 esting of the problems which bear upon the laws of 

 heredity among animals. 



NAUTILI. 



The Nautilus is extremely interesting, both on ac- 

 count of its chambered shell, and because the few 



