344 



MOLLUSCA 



The goiuuls of the always diivcious Ccplialopoda are unpaired and lie 

 far back in ihe \-ifceral sac. The duels in the female Octopoda (rarely 

 ill the males) and in se^me Decapoda (OiL,'opsida) are paired. In Xaiilihis 



onlv the rii^ht duct is fiuictional in cither 

 sex. although tlie left is well developed. 

 Elsewhere llrere is only the left duct. The 

 o\iducts are saccular with glaiulular walls; 

 independently of them two pairs of glar.ds 

 open to the exterior, the accessory glands 

 anil lite large nidame^ntal glands. 1 lie \as 

 deferens (lig. 35S) is more complicated. It 

 has swellings known as seminal ^■esicle, 

 prostate, and Xeedham's sac, in wliich the 

 spennatophores are stored. These latter 

 have such a complicated structure and 

 show such motions when swollen with 

 water that they -were long regardeil as para- 

 sitic worms (hg. 350). 



The spennatophores are con\eyed to 



honl. i7, ai;lomic sac passing the female liy means of more or less modi- 

 to tlie feft and above into the ,- i /i ^ ^ !• j\ i i 1 r ii 1 



pericardium; c, ccelomic canal 'i<?^l (hectocotyhsed) tentacles of the male, 

 to tfie vas deferens; J, vaa del'- In a few genera the whole tentacle becomes 



erens; (/', its openins; to cadom; . tt . ^ .^ 1 . /,- .- \ i. ii ^ •» 



/, portions of ccebm; «, Xeed- '^^ HectOCOtyluS (llg. 3O0). It swells at its 



hitni's pocket: /;', its mouth; base to a sac in wliich tlte peripheral end is 



p'. />- prostates; /, testis; /'.its , , „,, . ^ ... 



opening to cadom; r.v, sentin^d enclosed. 1 lus part, wluch contiuns a 

 vesicle. canal for the sp)ermatophores, 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 I'lrst 

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

 the hectocotvlization is not carried so far. 



Fig. 3 ^8. — ]\[a!e sexual organs 

 of Sepia offu-iihilis tatter Grol> 



^) 



Fig. 351). — Spcrmatophore of Si'pia drom TTatsclick, after Milne Edwards'). (J, dis- 

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



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

 gelatinous masses. Tliev are rich in yolk, and in con.se([uenee undergo partial 

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

 forms the anlagen of the .se])arate organs (eves, arms, siphon, and shell gland) 

 as flattened ])rojeetions. Later the embryonic body becomes distinct from the 



