13 



to the to]) of the keel, so as to form a bridge * over the cavity wliich con- 

 tains the eggs, the suckers corresponding to the tubercles, with the mem- 

 branes expanded over the shell and the arms floating in a horizontal mass, 

 as represented in Plate B. He describes the Argonaut as obtaining its 

 progress tlu-ough the element, shell foremost, not by any exertion of the 

 arms, but by the successive injection and ejection of water in and out of the 

 branchial cavity, the shell being firmly sustained witliin the embrace of 

 the velamentous membranes. 



The Argonaut shell, it may be observed, is not moulded on the body, 

 but is secreted from without, with little or no attachment to the animal ; 

 and, on this account, it was a long time before naturaKsts could bring their 

 minds to believe that the animal usually found in tliis shell was any other 

 than a parasite ; a naked octopod which took up its dwelling, like the Crabs, 

 in this particular kind of shell, of which the fabricator and lawful owner 

 had escaped detection. The matter has, however, been entirely set at rest 

 by the observations of M. Eang, above quoted, and by the praiseworthy 

 exertions of a lady, Madame Jeanette Power, resident at the port of Mes- 

 sina. She captured a number of Argonauts on the coast, and, keeping them 

 alive in a large cistern, performed such a course of experiments as left no 

 doubt of theii" relationship. It was noticed, for example, that the animal, 

 exactly at the moment of sexual stimulus, withdrew its body from the dis- 

 coid portion of the shell which it had hitherto filled, and there deposited 

 its eggs ; — that in twenty-five days after oviposition the young Argonaut 

 came forth from the egg, a naked octopod ; — and that in twelve days more 

 the two front arms became dilated at the extremity into a pair of membra- 

 nous webs, and commenced forming a thin fihny shell. 



These experiments were not, however, conducted without great perseve- 

 rance on account of the difficulty of preserving the animals ahve. The 

 cephalopodic nature of the Argonaut has been so fully estabhshed by the 

 enterprising researches of Madame Power, that it is quite unnecessary to 

 repeat the numerous arguments that have been since adduced in support of 

 her conclusions. The most remarkable is that recently put forth by M. 

 Deshayes, and derives additional interest from the circumstance of that 

 illustrious naturalist, together with M. De BlainviUe, having been for more 

 than fifteen years a supporter of the parasitic theory. " I have found," 

 says M. Deshayes, " a special system of secretion throughout the whole of 

 the anterior portion of the brachial membranes," and he goes on to relate that 

 the shell, upon being subject to a chemical analysis, proves to be composed 

 of two distinct laminse, different from that of the Gastropods ; and that the 

 calcareous portion being removed by acid, the parenchymatous residuum 



* La partie inferieure des deux grands bras, bien tendue, formait comma 2m font sur la cavite 

 laissee eutre le dos du mollusque et la portion rentrante de la spire on flottait I'extreniite d'une 

 grappe d'oeufs." — Raiuj, Documents pour scrvir a Vhist. nat. des Cc'phalopodes, p. 21. 



