344 



MOLLUSCA 



- n 



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. 358) is more complicated. It 

 has swellings known as seminal vesicle, 

 prostate, and Needham's sac, in which the 

 spermatophores are stored. These latter 

 have such a complicated structure and 

 show such motions when swollen with 



k 



water that they were long regarded as para- 

 sitic worms (fig. 359). 



The spermatophores are conveyed to 

 the female by means of more or less modi- 

 fied (hectocotylised) tentacles of the male. 

 In a few genera the whole tentacle becomes 

 a 'Hectocotylus' (fig. 360). It swells at its 

 base to a sac in which the peripheral end is 

 enclosed. This part, which contains a 

 canal for the spermatophores, cuts loose 

 from the male, and can creep about for days in the mantle chamber 

 of the female. Since it appears like an independent animal, it was first 

 described as a parasitic worm under the name Hectocotylus. In others 

 the hectocotylization is not carried so far. 



t 



FIG. 358. Male sexual organs 

 of Sepia officinalis (after Grob- 

 ben). a, ccelomic sac passing 

 to the left and above into the 

 pericardium; c, ccelomic canal 

 to the vas deferens; d, vas def- 

 erens; d', its opening to ccelom; 

 /, portions of ccelom; n, Need- 

 ham's pocket; n', its mouth; 

 p', p 2 , prostates; t, testis; t', its 

 opening to ccelom; t'5, seminal 

 vesicle. 



FIG. 359. Spermatophore of Sepia (from Hatschek, after Milne Edwards), a, dis- 

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



The eggs are either fastened singly to aquatic plants or are laid in large 

 gelatinous masses. They are rich in yolk, and in consequence undergo partial 

 discoidal segmentation (fig. 105). The blastoderm, on the end of the oval egg, 

 forms the anlagen of the separate organs (eyes, arms, siphon, and shell gland) 

 as flattened projections. Later the embryonic body becomes distinct from the 



