ARGONAUTID^. 23 



This genus derives its name from two large aquiferous 

 pores on the back of the head ; the arms are webbed. 

 Like Philonexis, Tremoctopus feeds on the mollusca of the 

 high seas, coming to the surface at the dusk of evening, 

 and pursuing its prey until the following morning ; there 

 are two species known, from the Mediterranean, and the 

 middle of the Atlantic. 



Species of Tremoctopus. 

 Quoyanus, B'Or'b. violaceus, Ftrus. 



Fam. AKGONAUTID.^. 



Arms subulate. The two upper or dorsal webbed at 

 the extremity, secreting (in the female) a symmetrical 

 involuted shell ; mantle supported by two buttons, fitting 

 into grooves at the base of the siphuncle. 



The male of the Argonaut is described by M. H. 

 Mliller as being much smaller than the female ; shell-less, 

 and with the superior arms not expanded as in the female, 

 but pointed. The most curious circumstance, however, 

 is the fact of a part developed within a coloured sac, 

 which occupies the place of the third arm, of the left 

 side ; this organ, which is an arm of the animal meta- 

 morphosed irregularly, is detached when the seminal 

 fluid formed in the true testes of the Argonaut has been 

 deposited in it, and from this moment it enjoys an 

 apparently independent life, and is the Hectocotylus of 

 Cuvier. " The Hectocotylus of the Argonaut, is then 

 the arm of a male Argonaut, metamorphosed for the 

 purpose of carrying the semen, and therewith impreg- 

 nating the female ; an arm endowed with so high a 



