406 



FISHES 



CHAP. 



In Protopterus each testis is divided into an anterior sperm- 

 producing part and a posterior tubular portion which has lost 

 the capacity of producing sex-cells. The testicular network is 

 greatly reduced, and forms but a limited connexion between the 

 tubular portion of the testes and the mesonephric duct (Fig. 

 233, B). If it be supposed that the testicular network became 

 still further reduced so that the connexion between the testes 

 and the kidney-duct took place directly through a single channel 

 instead of through several, the result would be a gouoduct 

 essentially similar to the male duct of an ordinary Teleost. 



ov 



-mn 



md f 



md 2 



U.S 



FIG. 233. Diagram to show the kidneys and gonoducts of a female Salmon (A), and of 

 a male Protopterus (B). i>ul l and md 2 , Anterior and posterior vestiges of the 

 Mullerian duct ; 1. 1, tubular posterior portion of the testis (t). Other reference 

 letters as in Fig. 230. (B, after Graham Kerr.) 



Should this view prove to be correct, it will follow that the 

 male gonoducts of all Fishes are differently -modified examples 

 of the Elasmobranch type. But there will still remain the 

 female gonoducts of Ganoids and Teleosts, which must be 

 regarded as distinct from Miillerian ducts unless it can be shown 

 that their different methods of development are not necessarily 

 fatal to their homology with Mullerian ducts, or that both types 

 of gonoduct can be derived from some intermediate type. 

 Assuming that some Fishes do possess male or female ducts 

 which have not been derived from the kidney system, but have 

 been independently acquired, there is still the question, which 

 of the two types is the more primitive, or, in other words, 

 has the Elasmobrauch type superseded the Teleostean, or vice 



