54 



MANUAL OF THE MOLLUSCA. 



I 



taining sufficient nutriment to support tlie embryo until it has 

 attained considerable size and development ; 

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

 half an inch long, consisting of several 

 layers, and the hulhnus 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 q^^. The embryonic development 

 of the cuttle-fishes has not been observed ; 

 t is probable that they would reveal more 

 curious changes than occur in any other class. 



The researches of John Hunter f into the embrj^onic condi- 

 tion of animals, led him to the conclusion that each dage in the 

 development of the highest animals corresponded to Wi^ 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- i 

 scribed, and may now be stated thus : — j 



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 moUusk, the insect, or the star-fish ; but only to the \ 



* Egg and young of hrdimus ovatus. Mull, sp., Bi'azil, 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 suffered to escape. At length, in the astonishing 

 ]xreparations for his museum, he constructed it, for the scientific apprehension, 

 out of the unspoken alphabet of natm-e." {Colendge.) 



