438 



MOLLUSCA. 



the female is further distinguished from the male by possessing a 

 shell. In Nautilus there are considerable differences in the number 

 and arrangement of the cephalic tentacles (see above p. 421) ; and in 

 all Dibranchs one of the arms of the male is different from the rest 

 and said to be hectocotylized (see p. 420). 



The sexual gland is single, and at the apex of the visceral sac, 

 It is in both sexes a special development of a portion of the 

 epithelium lining the genital division of the coelom. The sexual 

 cells are dehisced into the coelom and pass out by the genital 

 ducts, which open into the coelom and possess accessory glands on 

 their course. 



The generative duct of one side is usually suppressed or vestigial. 

 In Nautilus in both sexes the right duct persists, and the left is 

 vestigial, having lost its internal opening but retained the external. 

 In all male Dibranchs the left duct is alone present ; this is also 



the case in all females 

 excepting the Oeyopsida 

 and Odopoda (except 

 Cirroteutliis), in which 

 both oviducts are present 

 in functional develop- 

 ment. 



In Nautiliis the genital 

 coelom communicates with 

 the pericardial by three 

 openings in the septum 

 which separates them, and 

 the stomach and intestine 

 project into it. The genital 

 gland is a hollow structure, 

 and is to be regarded as a 

 folded -off portion of the 

 genital coelom, to the ante- 

 rior wall of which it is 

 attached ; it opens into the 

 genital coelom close to the 

 openings of this latter struc- 

 ture into the pericardium. 

 The reproductive cells are 

 produced from the lining 

 of the genital gland, and 



in the female the ripening ova, covered with their follicle cells and the flat 

 cells of the peritoneum, project into its cavity. In the male the walls of the 

 genital gland are folded so as to give rise to a number of branched tubes, 

 which open into the central cavity of the organ. The genital duct in both 



FIG. 352. Male sexual organs of Sepia officinal is (after 

 Duvernoy, modified from Grobben). T testis with a 

 piece of peritoneum ; To opening of the testicular tubes 

 into the coelom ; Td vas deferens ; opening of the 

 vas deferens into the body-cavity ; Vs vesicula seminalis ; 

 Pr prostate ; Sfi Needham's sac ; Oe generative opening. 



