494 Mb. j. graham kerb on [Nov. 19, 



of the view that the possession of such a network is a very ancient 

 characteristic of the gnathostomatous Vertebi-ata. Known long 

 to exist in Selachians, and in the Amphibia and Amniota, it is 

 now known to exist also in Ganoids (Lepidostevs, Acipenser, Amia) 

 and in the Dipnoi. It exists, in fact, in all the main divisions 

 except the Crossopterygians and Teleosts, Surely it is more easy 

 to believe that a secondary condition has come about in the last- 

 mentioned two groups than that the same condition should have 

 arisen secondarily in every one of the other groups mentioned ! 

 The probability of this being the case is, I beheve, much increased 

 bv considerations which will become apparent later on. 



' The points in the structure of the geuito-urinary apparatus 

 of the Dipnoi that appear to me to have a general bearing on the 

 morphology of the male genital ducts in other fishes are two : — 



(1) The testis, of a primitive very much elongated shape, has 



become divided into two regions : — an anterior sperm- 

 producing portion, and a posterior poi-tion which has lost 

 its sperm-producing function, has become simplified in 

 structure, and serves with its widely expanded cavities 

 merely as a vesicula seminalis and as a duct. 



(2) The testicular network has vanished throughout the 



anterior sperm-producing portion ; the posterior vesicular 



portion, on the other hand, retains its communication with 



the kidney apparatus near its posterior end. 



In these two features I believe we have a condition which throws 



much light upon the condition found in Teleostean Fishes and in 



Polypterus (as described by Budgett^ and Jungersen -), which, 



as Jungersen pertinently points out, leads up to the Teleostean 



condition. 



In Polypterus the testis is described as being continued back 

 into the testis-ridge (Budgett), containing the main testis-duct, 

 and associated with this a network of irregular cavities lined by 

 cubical epithelium and giving off here and there actecal projection. 

 At its hinder end the main cavity of this ridge communicates with 

 the kidney-duct near its posterior termination. 

 Similarly in Teleostei Jungersen ^ points out : — 



(1) That the genital duct of the male develops in complete 



continuity with the testis ; 



(2) That the genital duct in the male develops usually not as a 



simple tubular cavity as does the oviduct, but that a 

 network of anastomosing cavities is formed ; and 



(3) That the genital duct in the male usually develops its 



opening into the distal portion of the kidney-duct. 



Now the theoretical interpretation of the male genital ducts of 

 Crossopterygians and Teleosts is, I think, greatly facilitated by the 

 conditions which I have described as holding in Lepidosiren and 

 Protopterus. 



1 Trans. Zool. Soc. toL xv. Eead May 8, 1900, published April 1901. 



2 Zool. Anzeiger, June 14, 1900. 



■* Arb. Zool.-zoot. Inst. Wiirzbiirg, ix. 1889, p. 179. 



