PROF. OWEN ON THE ARGONAUT. 431 



that the corresponding muscles in the argonaut were very feebly developed, 

 and lost in the mantle, the absence of analogy between the two cephalo- 

 pods inclined me, in 1832, to consider as probable the parasitic theory ; 

 subsequently, however, the consideration of the absence of muscular adhe- 

 sion in the Carinaria, and of any adhesion at all in the Annelides which 

 secrete shells, deprived this argument of much of its force. 



" ' Secondly, M. de Blainville observes that ' the muscular integument 

 of the body of the cephalopod is not thinner than that of the naked species, 

 contrary to that which exists in all conchyliferous molluscs.' But what 

 mollusc, we may ask, has its whole body covered with a shell so delicate, so 

 transparent, so flexible and elastic, as is the shell of the living argonaut? 1 



" ' The dorsal border of the mantle is not free,' observes M. de Blainville. 

 Granted : and this would be undoubtedly strong proof that the cephalopod 

 of the argonaut did not secrete its shell, if it were not provided with other 

 organs for the purpose. In the pearly nautilus, on the other hand, which 

 has no veliferous arms, the dorsal border of the mantle is so produced that 

 it can be extended from the involuted spire, which it habitually covers, 

 over the whole exterior of the shell, just as the argonaut invests its shell 

 with the transparent films of the dorsal pair of arms : the analogy between 

 these two testaceous cephalopods is perfect, as regards their relative posi- 

 tion to the shell, but does not extend to their organs of secreting or of ad- 

 hering to the shell. 2 



"' The animal does not occupy the posterior part of its shell. This I 

 have ranged in the category of false facts, because the statement is only 

 applicable to the young animal. But granting it were true, as well might 

 we argue the Helix decollata to be a parasite, because it does not, like Ma- 

 gilus, retain and fill with shelly secretion the deserted spire of its shells ; 

 or that Magilus was a parasite because it did not secrete septa at regular 

 distances, like the Nautilus, or vice versa, as argue the argonaut to be a 

 parasite because it fills its vacated spire with mucus and with eggs.' 



" Finally, Mr. Owen proceeded to state in detail the points which still 

 remained to be elucidated in the natural history of this most interesting 

 mollusc. Among other experiments he suggested that the young argonaut 

 should be deprived of one of the velated arms, and preserved in a marine 

 vivarium, with the view to determine the influence which such mutilation 

 might have on the future growth of the shell : but in proposing further ex- 

 periments, and while admitting that the period of the first formation of the 

 shell yet remained to be determined, Mr. Owen stated that he regarded the 

 facts already ascertained to be decisive in proof that the cephalopod of the 

 argonaut was the true fabricator of its shell." 



*M. d'Orbigny truly states, " Les coquilles de 1 'argonaut n'ont pas la 

 contexture vitreuse des carinaires et des atlantes ; elles sont, au contraire, 

 demi-cornees, flexibles ; et nous n'en trouvons l'analogue dans aucun autre 

 des mollusques." — Loc. cit. p. 11. 



2 " Messrs. de Blainville and Gray conceive me to be in error in the po- 

 sition I have assigned to the pearly nautilus in its shell, but their argu- 

 ments on this point are based on the same hasty generalization that has led 

 to the hypothesis of the parasitism of the argonaut. Judging from the ana- 

 logies which have been cited in support of their views, it would have been 

 equally reasonable to have called in question the accuracy of the relative 

 position which I have assigned to the soft parts of Terebratula and Orbi- 

 cula, viz., with the ven'tral surface applied to one valve, and the dorsal sur- 

 face to the other, because in the lamellibranchiate bivalves one valve cor- 

 responds to the right, and the other to the left, side of the animal. 



