66 MANUAL OF THE MOLLUSCA. 



slickers, 45 on each side ; but no branchia ; the skin contains numerous 

 changeable spots of red or violet, like that of the argonaut.* 



According to the observations of Madame Power, " the newly hatched 

 argonaut has no shell, and is quite unlike what it afterwards becomes ; it is a 

 sort of little worm, having two rows of suckers along its length, with a fili- 

 form appendage at one extremity, and a small swelling at the other. It might 

 be supposed to represent an extremely small bmchial appendage, from which 

 the other parts were afterwards to be developed."! (Kolliker.) 

 FAMILY I. AllGONAUTID^E. 



Dorsal arms (of the fern ale> webbed at the extremity, secreting a symme- 

 trical involuted shell. Mantle supported in front by a single ridge on the 

 funnel. 



Genus AKGONAUTA, Lin. Argonaut or paper sailor. 



Etymology., argonautai, sailors of the ship Argo. 



Synonyms, ocythoe (Rafinesque). Nautilus (Aristotle and Pliny). 



Example, A. hians, Soland, pi. II., fig. 1. China. 



Fig. 32. Arg^naufa argo L. swimming .t 

 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 unoccu- 

 pied hollow of the spire serves as a receptacle for the minute clustered eggs. 

 The argonaut sits in its boat with its siphon turned towards the keel, and its 

 sail-shaped (dorsal) arms closely applied to the sides of the shell, as in fig. 32, 

 where, however, they are represented as partially withdrawn, in order to show 

 the margin of the aperture. It swims only by ejecting water from its fun- 



* Similar instances of a permanently rudimentary condition of the male sex, oc- 

 cur amongst the lowest organized parasitic crustaceans; the males of achtheres, ler- 

 nceopoda, tracheliaster, fyc., are frequently a thousand times smaller than the female, 

 upon whom they live, and from whom they differ both in form and structure. 

 Gosse has described a similar disparity of the sexes in asplanchna. 



t An. Sc. Nat. 2 Series, vol. 16, p. 185. 



t From a copy of Rang's figure, in Charlesworth's Magazine; one-fourth the na- 

 tural size ; the small arrow indicates the current from the funnel, the large arrow th ; 

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



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

 shell with the nucleus reversed, implying that the animal had turned quite round in it> 

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



.V 



