162 MANUAL OF THE MOLLUSCA., 
Example, A. hians, Soland. Pl. I1., Fig. 1. China. 
The shell of the argonaut is thin and translucent; it is not 
moulded on the body of the animal, nor is it attached by shell- 
muscles; and the 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 special 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 Zanthina. 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 Fig. 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however, they are represented as partially withdrawn, in order 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 reyersed position, carry- 
ing its shell over its back like a snail. (Madame Power and 
M. Rang.) 
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 yiolet 
coloured capsule on its back. The sac never contains more 
than one Hectocotylus, which is attached by its base, whilst 
* From a copy of Rang’s figure, in Charlesworth’s Magazine; one-fourth the 
natural size ; the small arrow indicates the current from the funnel, the large alrow 
the direction in which the “sailor” is driven by the recoil. 
7 Poli has represented it sitting the opposite way; the writer had once an argonaut 
shell with the nucleus reversed, implying that the animal had twned quite round in its 
shell, and remaincd in that position, The specimen is now in the York Museum, 
