238 



COMPARATIVE ANATOMY 



CHAP. 



female ducts nearly always unite in the base of a genital cloaca, which often lies 

 anteriorly on the right, on a papilla. The male and female apertures are rarely 

 separate ; when tliey are so, they lie close together {cf. Fig. 195 of Phyllirhoe). 

 The penis is often armed in various ways. 



The important subject of the mutual relations of the three types of genital ducts 

 in hermaplirodite Gastropoda has been much discussed, but no satisfactory con- 

 clusion has been reached. Ontogenetic research has been appealed to so far in vain. 



It is thus not at present known whether the 

 single hermaphrodite duct lias arisen by the 

 fusing of separate male and female ducts, or 

 whether the separate ducts have come into exist- 

 ence by the S2)litting of an originally single 

 hermaphrodite duct. The difficulty is increased 

 by the fact that the genetic significance of the 

 hermaphrodite gland is uncertain. 



Fertilisation is mutual in hermaphrodite 

 Gastropods. It is, however, certain that, in the 

 Pulmonata at least, when copulation does not 

 take place, self - fertilisation can occur. The 

 hermaphrodite duct not infrequently carries one 

 or two lateral c?eea or vesiculiB seminales, in 

 which an animal can store up its own sperm to 

 be used in fertilising its own eggs if cross-fertil- 

 isation does not take place. The eggs and the 

 sperm are often not ripe at the same time. 



(2) Cephalopoda. — Although the gonad in all 

 extant Cephalopoda is unpaired, the ducts are 

 Pio. 195.-Geiiital organs of Phylli- originally paired in both sexes. In Nautilus, 

 rhoe (after Souleyet). 1, Vas deferens ; the Oegopsidcc, and the Odopoda, there is one 

 2, penis ; 3, oviduct ; 4, male, 5, female pair of ducts in the female ; but in the males a 

 genital aperture ; 6, vagina ; 7, herma- -^^^ seminal duct occurs only in Nautilus and 

 plirodite gland ; 8, liermaphrodite duct ; _, ■, • ,m j % t ht- aw 



9, receptaculum seminis. Philonexis carcuc {Treimdopus). In Nautihis, 



in which both sexes possess paired ducts, the 

 left duct is in both cases rudimentary and no longer functions. It is the so-called 

 pear-shaped vesicle, which is attached on one side to the heart and the lower end 

 of the gonad, and on the other opens into the mantle cavity at the base of the 

 lower gills. 



Where only one duct is retained, it is, in l)oth sexes, the one on the left, as in 

 Loligo, Sepia, Scpiola, liossia, Scpioteuthis, Chiroteuthis, Cirrhoteuthis, etc. 



The genital ducts rise on the wall of that part of the secondary body cavity which 

 is known as the genital cavity (peritoneal sac, genital capsule), and open into the 

 mantle cavity at the sides of the anus, between the nephridial aperture and the base 

 of the gills. 



Male ducts, seminal duct. — In the more comiilicated form of male duct, 

 such as that of Sepia (Fig. 196), four principal divisions may be distinguished. 

 From the testicular capsule rises a vas deferens, which runs along in close coils, and 

 then widens into a vesicula semiualis, the highly developed and much folded epi- 

 thelium of wdiich plays an important part in the formation of the spermatophores. 

 The vesicula semiualis is continued as a thin vas deferens to the last division, the 

 spermatophoral pouch (Needham's pouch), which serves as a reservoir for the 



