ARGONAUTA ARGO AND THE HECTOCOTYLI. 61 



it adheres to the mantle. In the capsule lies a white mass which 

 consists of little cylinders or caeca which are united at one ex- 

 tremity: their length is about 1 Hne, their thickness 0-06--1 

 of a line. A clearly-defined tunica propria could not be distinctly 

 recognized in these spirit specimens for each cylinder, but ex- 

 panded membranous coverings could be frequently observed 

 between them. In the cylinders themselves large pale cells lay 

 at the periphery ; the interior was in one case occupied by masses 

 which consisted of numerous granules of about 0-002 of a line 

 in diameter, and which had frequently a delicate process in an 

 oblique direction with regard to the axis of the cylinder. In a 

 second specimen there could be no doubt that these lumps were 

 forms of the development of the spermatozoa. There lay in the 

 same position more or less developed bundles of spermatozoa, 

 whose somewhat wavy threads had the same oblique direction 

 with regard to the axis of the little cylinder. This appeared, 

 consequently, to be quite a fibrous streak. The length of the 

 single bundles was about 008 of a line. 



In these two animals provided with full testes, the generally 

 white and distended capsule of the Hectocotylus was colourless 

 and collapsed. In a third animal again, which had carried the 

 detached Hectocotylus-arm filled with spermatozoa, the shining 

 golden capsule was indeed present, but it was empty. If we 

 connect all these facts together, it becomes very probable that the 

 semen is produced in the testis, and that it is then transferred 

 into the Hectocotylus, although I could not recognise with cer- 

 tainty this portion of the ductus deferens, which must lie under 

 the skin of the head. 



The silvery capsule, then, would be neither penis nor testis, 

 but vesicula seminalis ; and so long as the Hectocotylus remains 

 connected with the rest of the animal, the essential distinction 

 from other cephalopod males must consist in this, that the aper- 

 ture of the ductus deferens, instead of lying in the mantle- cavity, 

 is placed at the end of the peculiarly-developed arm. 



The structure of the silvery capsule harmonizes very well with 

 Ihis interpretation. It is, as KoUiker has shown, very muscular *, 

 and in its interior there lay in all the free, and in the largest of the 



* The musculav fibres are distinguished from those of the rest of the body by 

 a peculiar development, a point to which I shall recur elsewhere. 



