336 ME. J. S. BUDGETT ON TJIE STRUCTURE 



fniwiiid l>v Sicbold iiiid by Urock, tliat in certain Teleosteans in which flie testes are 

 linllow, tlie cavity of tlie testis, and therefore probably also of the testis-duct, is formed 

 by a fiilding-off of a portion of the coelom. 



Jungersen came to the conclusion that in all Vertebrata except Elasmobranchs the 

 oviducts were homologous and formed by a folding-off of a groove in the coclomic wall. 

 If this conclusion is correct, then there is a difficulty in the way of the view I have put 

 forward which it is not easy to overcome. In many forms which possess a testicular 

 network there is also found, in the male, a more or less rudimentary female genital 

 duct usually called a MiUlerian duct. It seems unlikely, then, to say tlie least of it, 

 that, in tiiese forms, the longitudinal canal of the network in the male and the genital 

 duct of the female can be homologous, for these structures occur side by side in the 



males. 



If the ducts of Ganoidei and Teleostei really are homologous in the male and female, 

 Avhile in the other Gnathostornata they are not homologous, then either the female 

 duct or the male duct cannot be homologous throughout the Gnathostomata. 



It can, I think, hardly be doubted that the male and female ducts in Teleostei are 

 homologous. I have before given reasons for thinking that they are so in Polnpterus. 

 It remains, then, to decide whether it is more likely that the male duct in Polyptcrus is 

 homologous with the longitudinal canal of Lejndosfeus and so with that of other forms 

 in which a testicular network occurs, or that the female duct in Ganoidei, Crossopterygii, 

 and Teleostei is homologous with the female duct of other Gnathostomata, as held by 

 Jungersen. 



The male duct of Polypterus lies in exactly the same position as the blind longitu- 

 dinal canal of Lepidosteus, and it is difficult to avoid the conclusion that these ducts 

 are homologous with one another, and again that this canal in Lepidosteus is the 

 longitudinal canal of the testicular network of other forms. 



Jungersen ^ admits this comparison, but derives the male duct of Polypterus and 

 Teleostei from the fusion of a testicular network with the loss of its connection with 

 tiae kidney, which he, with Semon ^ and Kerr ^ and many other authors, regards as the- 

 primitive condition. But Jungersen ■* also holds that the female ducts are homologous 

 throughout the Gnathostomata. The presence of the rudimentary Miillerian duct in 

 many forms with a testicular network makes it impossible on this view to regard the 

 ducts of male and female in any vertebrate as homologous structures, as they appear to 

 be in Teleostei. 



Supposing, however, that the female ducts in Pohjptems, Ganoidei, and Teleostei are 

 not homologous with those of Elasmobranchii and xlmniota, as their position in the 

 hind end of the body-cavity, and the presence in Puhjptems and Lepidosteus of 



^ Zool. Anz. xxiii. Bd. No. 617. ' Jen. Zeitschr. 1891. 



' Proc. Zool. Soc. lyOl, vol. ii. p. 493. ■■ Arb. Inst. Wiirzburg, Bd. ix. 1SS9. 



