41 



accordance with Madame Power's belief that the Cephalopod was the 

 true constructor of the shell, while no contradictory inference had 

 been, or could be, deduced from an examination of the specimens 

 themselves. 



With reference to the second suite of specimens, viz. the ova of 

 the Argonaut in different stages of development, Mr. Owen entered 

 into a detailed account of the new and interesting facts which they 

 revealed. In the ova most advanced, the distinction of head and 

 body was established ; the pigment of the eyes, the ink in the ink- 

 bladder, the pigmental spots on the skin, were distinctly developed ; 

 the siphon, the beak,— which was colourless and almost transpa- 

 rent, — and the arms were also discernible by a low microscopic 

 power ; the arms were short and simple ; the secreting membranes 

 of the shell were not developed, and of the shell itself there was no 

 trace. 



In the second memoir of 1838, published by Madame Power, it is 

 stated that the young Argonaut is excluded from the egg, as such, 

 but naked, twenty-five days after oviposition, and that in ten or 

 twelve days more, she discovered that they had formed their little 

 shell. Mr. Owen regretted that there were no specimens in the 

 present collection exhibiting the commencing formation of the shell ; 

 these were still a desideratum : but he proceeded to say, that the ob- 

 servations on the development of the ova of the Mollusca in general, 

 which science possessed, would be greatly overstated, if one per cent, 

 of the known species of Mollusca were allowed to have been subjected 

 to such examination ; he could not, therefore, admit, or indeed under- 

 stand, the philosophy of regarding the period of the development of 

 a mere dermal production, like the shell, as being subject to so pre- 

 cise a law, that its non-appearance in an embryo-mollusk, prior to 

 its exclusion from the egg- covering, was to be considered proof po- 

 sitive that such mollusk should never thereafter have the power of 

 secreting a shell. Now it was evident, from the observation of Ma- 

 dame Power's specimens, independently of any statements respecting 

 them, that the expanded membranes of the dorsal pair of arms are 

 not formed until the development of the embryo has far advanced : 

 if, therefore, these membranous arms be, as Madame Power states, 

 the organs of the secretion of the shell, that shell may not be formed 

 until after the exclusion of the young Argonaut. 



The proof that the velated arms possess, like the expansions of 

 the mantle of the Cyprsea, a calcifying power, was afforded by the 

 tl:ird series of specimens on the table of the Society. These consist- 

 ed of six shells of the Argonaut, from which Madame Power had 

 removed pieces of shell while the Argonauts were in life and vigour, 

 in her marine vivarium. One of the shells had been removed from 

 the. animal ten minutes after the fracture; another Argonaut had 

 lived in the cage two months after being subjected to the experi- 

 ments : the remaining specimens exhibited intervening periods be- 

 tween the removal of a poition of the shell and its reparation. The 

 fractured shell first described had the breach repaired by a thin 

 transparent membranous film : the piece removed was taken from 

 the middle of the keel. In a second specimen calcareous matter 



