54 



MANUAL OF THE MOLLUSCA. 



taining sufficient nutriment to support the embryo until it lias 

 attained considerable size and development ; 

 tlius, the newly-born cuttle-fish has a shell 

 half an inch long, consisting of ^ several 

 layers, and the bulimus ovatus has a shell 

 an inch in length when hatched. (Fig. 31.) 

 These are said to undergo no transforma- 

 tion, because their larval stage is concealed 

 in the e,g^. The embryonic development 

 of the cuttle-fishes has not been observed ; 

 ^" it is probable that they would reveal more 



curious changes than occur in any other class. 



The researches of John Hunter ^ into the embryonic condi- 

 tion of animals, led him to the conclusion tliat each stage in the 

 development of the highest animals corresponded to \hQ perma- 

 nent form of some one of the inferior orders. This grand gene- 

 ralisation has since been more exactly defined and established by 

 a larger induction of facts, some of which we have already de- 

 scribed, and may now be stated thus : — 



In the earliest period of existence all animals display one 

 uniform condition ; but after the first appearance of special de- 

 velopment, uniformity is only met with amongst the members of 

 the same primary division, and with each succeeding step it is 

 more and more restricted. From that first step, the members 

 of each primary group assume forms and pass through phases 

 which have no parallels, except in the division to which each 

 belongs. The mammal exhibits no likeness, at any period, to 

 the adult mollusk, the insect, or the star-fish ; but only to the 



* Egg and young of hulimns ovatns, INIull. sp., Brazil, from specimens in 

 the collection of Hugh Cuming, Esq. 



t " In his printed works the finest elements of system seem evermore to 

 flit before him, twice or thrice only to have been seized, and after a momentary 

 detention to have been again >sutTered to escape. At length, in the astonishing 

 preparations for his museum, he constructed it, for the scientific apprehension, 

 out of the unspoken alphabet of natm'e." {Coleridge) 



