ARGONAUTA ARGO AND THE II ECTOCOTYLI. 89 



(D. Ch.) in a pedunculated sac in the place of the third arm of 

 the left side. 



3. The thick end of the Hectocotylus is fixed to the pedicle, 

 while the thin coiled-up part is free. 



4. By the bursting of the sac and the eversion of its edges, 

 the pigmented capsule on the back of the Hectocotylus arises. 



5. The testis lies in the abdomen of the whole animal, the 

 external aperture of the ductus deferens being near the point 

 of the Hectocotylus-arm, whose thin appendage has at the same 

 time the function of a penis. 



6. In the axis of the Hectocotylus there lies a chain of 

 ganglia. 



7. It is not to be supposed that the Hectocotyli are developed 

 as vermiform embryos in especial bunches of ova. 



8. The Hectocotylus Octopodis of Cuvier, which Verany has 

 shown to be the arm of an Octopus, is mainly distinguished from 

 the Hectocotylus Argonauts by its size, by the presence of a 

 capsule at the free end, and by its development as the third arm 

 on the right side, of the Octopus. 



9. The Hectocotylus Tremoctopodis of Kolliker is distinguished 

 by its gills, by a peculiar structure of the ductus deferens, and 

 by the want of a pigmented dorsal capsule ; but it possesses a 

 ganglionic chain in its axis, its penis is a more delicate prolon- 

 gation of this, like the appendage of the Hectocotylus Argonaulce, 

 and its cleft abdominal capsule is to be compared to the lobe 

 upon the appendage of the latter. 



10. The Hectocotylus Tremoctopodis is thence to be considered 

 analogous to the two other Hectocotyli) although the animal as 

 whose arm it is developed is not at present known. 



11. Each Cephalopod with a Hectocotylus-arm is to be re- 

 garded as the male of the corresponding female Cephalopod. 



12. The Hectocotyli are intended to separate from the rest of 

 the body, and are then received and lodged by the female. 



13. In this condition they have apparently independent mo- 

 tion and circulation ; they contain perfect semen ; and in Trem- 

 octopus, as also probably in Argonauta, a copulation with the 

 female animals takes place. 



14. The Hectocotyli are not comparable to the spermatophora 



