372 



and, as these do not inhabit shells, the membranes, even if they 

 could be kept erect, could not be used for wafting the animal 

 along the water. It seems to be beyond question that these 

 expanded arms are not locomotive organs. Madame Power,* who 

 examined a great number of these animals at Messina, from the 

 position of the animal in the shell, with these arms to the right 

 and left, and from repeatedly w-atching its movements, has ascer- 

 tained that it can drag itself along the bottom, or climb madre- 

 pores in search of food, or anchor itself, by the suckers of the 

 other arms, hanging from its shell, which is carried above it 

 supported by the membranous arms. According to Von Siebold,t 

 these dorsal arms, with their terminal cutaneous lobes, are used 

 for keeping the shell in place by their application to its external 

 surface, their movements, as in other Cephalopods, being chiefly 

 due to the contractions of the mantle and the funnel; — it is 

 certain that they can move forwards and laterally, to a certain 

 extent, by the action of their arms ; else they would seem poorly 

 provided with means for obtaining their prey. As will be seen 

 hereafter, the shell is principally secreted by these arms, whose 

 two surfaces have a different structure ; the external surface is 

 quite smooth with many chromatic or coloring cells ; while the 

 internal has hardly any, but is covered with numerous reticulated 

 projecting lines, becoming more prominent as the lobes are con- 

 tracted, and between which are cell-like depressions. 



The Argonaut has no internal shell like the Cuttle-fish, but an 

 external, monothalamous, symmetrical shell, containing but not 

 attached to its body, either by a siphon or by muscles, as in the 

 Nautilus. The eggs are deposited in the cavity of the shell, as 

 in the specimen exhibited. 



The arms are not fully united by membranes at their base, as 

 in the Poulp, so that the Argonaut is without the powerful loco- 

 motive organ furnished by the contraction of these webs. Zoolo- 

 gists were for a long time divided in opinion as to whether the 

 Argonaut shell is formed by the animal found in it ; the arguments 

 on both sides will be given hereafter. In the Nautilus, power- 

 ful muscles take their origin from the central cartilage, and form 



* Report of Brit. Association, 1844, pp. 74-7, London, 

 t Burnett's Translation, p. 276, Boston, 1854. 



