THE CEPHALOPODA 321 



no internal communication with the coelom. The artery of the 

 pyriform sac forms a symmetrical pair with that of the right 

 gonaduct, so that there can be no doubt as to the homology of the 

 former organ. On the other hand, all the male Dibranchia and 

 the females of Spirula, the Myopsida and the Cirrhoteuthidae, have 

 a single gonaduct, and this always on the left side (Fig. 272, g). 



The ovaries and testes, as well as their ducts, are strictly com- 

 parable with one another from a morphological point of view, but 

 they differ somewhat in structural details. The ovary is simply 

 a portion of the wall of the coelom from which the ova originate. 



...R.G.O 



L.G.O 



FIG. 284. 



Diagrams of the male and female generative organs of the pearly Nautilus, to show the 

 relation of the rudimentary duct of the left side to the testis and ovary respectively, and of the 

 cardiac ventricle to the organs of both sides. Ventral aspect. Ac, accessory gland of the male 

 apparatus ; Alb, albuminiparous gland of the female apparatus ; Fo, foramen in the membrane 

 which attaches the pyriform appendage to the ventricle and to the testis or ovary (this foramen 

 places two portions of the viscero-pericardial sac in free communication with one another) ; 

 L.G.O, left genital orifice; N, Needham's sac in the male, in which the spermatophores an> 

 formed ; 0, ovary ; P, penis ; Pyr, Owen's pyriform appendage, attached by a membrane to the 

 ventricle of the heart, and also txi the testis or ovary ; R.G.O, right genital orifice ; T, testis ; 

 V, cardiac ventricle, with its four branchial veins. (After Ray Lankester and Bourne.) 



This region generally forms a conspicuous projection, into which the 

 coelomic epithelium is deeply invaginated in such a manner as to 

 constitute an ovarian cavity communicating with the genital coelom 

 by a narrow aperture. The ova that originate from the wall of 

 this ovarian cavity are no longer superficial cells of the wall itself, 

 but have emigrated below the ovarian epithelium, have grown in 

 size, and have come to project into the cavity of the ovary, carry- 

 ing the epithelium before them, in the same manner as the ova of 

 many Amphineura and of Pseudokellya. The ova which thus lie 

 beneath the true coelomic epithelium also become surrounded by 

 an interior follicle formed at the expense of the cells in their 



