iv TELEOSTEAN OVARY 277 



probability seems on the whole in favour of the first mentioned, for 

 the formation of folds or grooves of the fertile surface of the genital 

 fold, so as to give increased area, is a very usual phenomenon, and 

 the formation of a single longitudinal groove would readily lead to the 

 first-mentioned condition. On the other hand the replacement of 

 this condition by the second is also readily understandable. 



The ovary passes without a break into the oviduct which is 

 simply the posterior sterile portion of the genital ridge in which a 

 cavity develops secondarily — not always continuously — from before 

 backwards. The oviduct differs greatly in length in different 

 Teleosts : in some (Zoarces, Cyclopterus) the ovary itself may stretch 

 right back to the genital pore. 



Although the above description fits in with the normal con- 

 ditions, there are various Teleosts in which the processes of fusion 

 connected with the ovary do not take place and in which the ovary 

 remains as a genital fold hanging down into the splanchnocoele, 



Fig. 142. — Diagram illustrating the conversion of the genital fold into a closed ovary 

 in the Teleostean fishes. 



e.g. in the case of the Salmon fusion of the ovarian edge with the 

 body wall takes place anteriorly for a short distance and again in 

 the posterior sterile region, but the greater part of the fertile 

 region of the ovary hangs free. In such cases the eggs are shed 

 into the splanchnocoele and pass to the exterior by genital pores 

 (compare Cyclostomata, p. 246). 



Unfortunately we are still in ■ almost complete ignorance regard- 

 ing the development of ovary and oviducts in the Ganoids. From 

 the little we do know it would appear that in Zepidosteus (Balfour & 

 Parker, 1882) the ovary becomes enclosed in the same manner as 

 in Cyprinoids (Fig. 142, B). Posteriorly it is continuous with the 

 oviduct as in Teleosts generally. In the other Ganoids the ovary 

 retains the form of a genital fold hanging down into the splanchno- 

 coele while the oviduct is provided anteriorly with a coelomic 

 funnel. The position of this funnel, far removed from the front end 

 of the splanchnocoele, is sometimes used as an argument against 

 the homology of this opening with the ostium of a true Mullerian 

 duct, but such an argument carries little weight as we know from 



