392 



MOLLUSC A. 



of the pericardium around the systemic and branchial hearts and the thin- 

 walled genital sac, one wall of which bears the genital ducts, while on the 

 other the sexual cells arise or the ducts of a separate sexual gland open 

 (fig. 392). 



The gonads of the always dioecious Cephalopoda are unpaired 

 and lie far back in the visceral sac. The ducts in the female 

 Octopoda (rarely in the males) and in some Decapoda (Oigopsida) 

 are paired. In Nautilus only the right duct is functional in 

 either sex, although the left is well developed. Elsewhere there 

 is only the left duct. The oviducts are saccular with glandular 

 walls; independently of them two pairs of glands open to the 

 exterior, the accessory glands and the large nidamental glands. 

 The vas deferens (fig. 392) is more complicated. It has swellings 

 known as seminal vesicle, prostate, and Needham's sac, in which 

 the sperm atophores are stored. These have such a complicated 



FIG. 393. Spermatophore of Sepia. (From Hatschek, after Milne Edwards.) a, dis- 

 charging apparatus ; 6, packet of spermatozoa ; c, envelope. 



structure and show such motions when swollen with water that 

 they were long regarded as parasitic worms (fig. 393). 



FIG. 394. Male of Argonnuta argo. (After Miiller, from Hatschek.) J-A, arms of right 

 side ; !.-., arms of left side ; 3, hectocotylised arm, at the left in its sac, at the 

 right protruded. 



The spermatophores are conveyed to the female by means of 

 more or less modified (hectocotylised) arms of the male. In a few 

 genera the proper tentacle becomes a ' Hectocotylus ' (fig. 394). 



