44 



spire of the shell should be manifested ? Why should it not be made 

 subservient to the generative economy of the species ? Yet, because 

 it is neither solidified, decollated, nor camerated, it is argued in 

 the third place, that the Argonaut shell must have been secreted by 

 some other MoUusk than the Cephalopod usually found in it. 



"4thly. Mr. Gray observes, ' the young shell of the just-hatched 

 animal, which forms the apex of the shell at all periods of its growth, 

 is much larger (ten times) than the eggs contained in the upper 

 part of the cavity of the Argonaut.' The argument here founded on a 

 comparison of the size of the supposed nucleus of the Argonaut shell 

 with that of the ovum of the Ocythoe, has been quoted with appro- 

 bation by M. de Blainville ; but granting that the shell of a testa- 

 ceous MoUusk is always formed before the embryo is excluded from 

 the ovum, (which, as I have already shown, is a postulate, and not 

 an established law) the force of an argument for the parasitic 

 theory, based on this postulate, wholly depends upon another 

 assumption, viz. that the ovum of a Mollusk never enlarges after 

 it has quitted the parent. Now, the first observation which the 

 promulgator of this argument had the opportunity of making on 

 one of our commonest littoral Testacea — the Whelk, proved to him 

 that the molluscous ovum in that species does enlarge after exclu- 

 sion, and Mr. Gray was subsequently compelled to admit ' that the 

 size of the nucleus would not offer any difficulty with respect to the 

 Ocythoe being the maker of the shell which it inhabits*.' 



" Whether the other arguments founded by Mr. Gray upon the 

 form of the body, and the want of perfect adaptation or adhesion of 

 the body to the shell, &c., are unanswerable, as that experienced Con- 

 chologist states that he considers them to be, must depend upon 

 the degree of weight which the objections above advanced are allow-, 

 ed to carry. 



" With respect to the conclusions as to the parasitism of the Ocy- 

 thoe, drawn from observing the relation of the Cephalopod to its 

 shell, their insufficiency depends upon the circumstance that in 

 forming them the condition of the mature Argonaut has been con- 

 sidered as applicable to every period of its life, and the arguments 

 Nos. 1 and 2 being founded upon that supposition, thereby fall to 

 the ground. In the argument for the parasitic theory deduced from 

 the development of the Argonaut shell, a general rule, applicable 

 to an extensive primary division of the animal kingdom, is assumed 

 from the result of extremely scanty observations, which are altogether 

 inadequate to its establishment. 



" In the Proceedings of the Zoological Societyforl837,Mr. Charles- 

 worth proposed an argument in favour of the parasitism of the Ocy- 

 thoe, which has the merit — not possessed by those above discussed—" 

 of being founded on the observation of a new fact in the natural hi- 

 story of the Argonaut, viz., that breaches in the shell were repaired 

 by a substance agreeing in every respect with the original shell. 

 Mr. Charlesworth has, however, since admitted that this fact is not 



• Magazine of Natural History, New Series, 1837, p- 248. 



