102 MANUAL OF THE MOLLUSCA. 



Example, A. Hans, Soland. PL II., Fig. 1. Cliina. 



Tlie shell of tlie argonaut is thin and translucent ; it is not 

 moulded on tlie body of tlie animal, nor is it attached by sbell- 

 mu.scles ; and tbe unoccupied hollow of the spire serves as a 

 receptacle for the minute clustered eggs. The shell is believed 

 to be peculiar to the female. Its spacial function is for protec- 



Fig. 37. Argonauta argo L, swimming.* 



tion and incubation of the eggs. It is not homologous with 

 the chambered or internal rudimental shells of other cephalo- 

 pods, but may be compared with the cocoon of the leech, or the 

 float of lantliina. The argonaut sits in its boat with its siphon 

 turned towards the keel,t and its sail-shaped (dorsal) arms 

 closely applied to the sides of the shell, as in Eig. 37, where, 

 however, they are represented as partially withdrawn, in order 

 to show the margin of the aperture. It swims by ejecting 

 water from its funnel, and crawls in a reversed position, carry- 

 ing its shell over its back like a snail. (Madame Power and 

 M. Eang.) 



The male argonauts are one inch in length, and possess no 

 shell ; their dorsal arms are pointed, not expanded. The testis is 

 large, and like that of the Octopus in structure and situation ; 

 it contains spermatozoa of different degrees of development, 

 and the excretory duct probably debouches into the Hecto- 

 cotylus. The sac in which the Hectocotylus is developed is 

 cleft by the movements of the Hectocotylus in extending 

 itself, while the sac becomes inverted, and forms the violet 

 coloured capsule on its back. The sac never contains more 

 than one Hectocotylus, which is attached by its base, whilst 



* Froin a copy of Eang's figure, in Charle&wortK' s Magazine; one-fourth the 

 natural size ; the small arrow indicates the current from the funnel, the large arrow 

 the direction in which the "sailor " is driven by the recoil. 



t Poli has represented it sitting the opposite way; the writer had once an argonaut 

 eTiell with the nucleus reversed, implying that the animal had turned quite round in its 

 eliell, and remained in that position. The specimen is now in the York Museum. 



