SEXUAL ORGANS. Ill 



In the Cephalopoda and the prosobranchiate gastropods the 

 sexes are distinct (dioecious >, but they are united in the same 

 individual in most of the other mollusks (monfficious). The 

 Cephalopoda and prosobranchiates pair, the monoBcious land 

 snails require i^ciprocal union; the limneids unite in succession, 

 forming floating chains ; in the lamellibranchiatesthe spermatozoa 

 are discharged into the water, whence they are inhaled with the 

 respiratory currents. 



Cephalopoda (xvi, 84-87, 90,92\ The sexes are distinct, and 

 in some of the genera at least, the female individual is the largest 

 and readily distinguishable externall3^* The reproductive 

 organs are lamellar or branched ; their cellular contents are 

 metamorphosed into ova or spermatozoa^ which are attached to 

 the wall of a chamber communicating with the pallial cavity by 

 one or two ducts, which, in the female present glandular enlarge- 

 ments. Upon the walls of the branchial cavity of the female 

 two niclimental glands are developed ; besides, sometimes 

 accessory glands, within which is secreted a viscid fluid which 

 envelops the ova and aggregates them into various forms, 

 differing according to the genus. 



In the male the cases or spermatophores 'Xvi, 92), containing 

 the spermatozoa are furnished by a prostatic gland. These 

 spermatophores, in the dibranchiata are ovate, cylindrical and 

 narrow, consisting of a thin case, ending sometimes in a filament 

 at one end ; at the other or thicker end is contained a sack full 

 of spermatozoa, to which is attached an elastic spiral cord, coiled 

 and compressed within the balance of the case. Upon coming- 

 in contact with the water these spiral bodies commence moving 

 and finally burst through the thin end of the investing spermato- 

 phores dragging with them their sacks of spermatozoa. 



In Nautilus, Van der Hoeven has ascertained that the structure 

 of the spermatoiDhores is much more simple. In this genus the 

 oviduct arises from a chamber which communicates with that in 

 which the ovary is lodged. A large albumen-gland opens into 

 the latter. So also the vas deferens, instead of originating 

 directly from the sack of the testes, communicates with it 

 through an intervening chamber. 



The most curious portion of the sexual history of the dibran- 



* The sexes in Sepia officinalis may be readily externally distinguished. 

 There is in the first place a diiference of coloration, the females being 

 unicolored, whilst the males have zebra like markings across the marginal 

 fins and the dorsal arins- especially when irritated. But the best means 

 of distinction is in the relative lengths of head with the aims and body ; 

 in the males these two dimensions are about equal, hut in the females the 

 body is only two thirds the length of the head and arms. The cuttle bone 

 in the female is much wider at d more excavated behind.— Eert, Mem. 

 Linn. Soc. Bordeaux, v, 118. 



