iv UEINOGENITAL CONNEXION 279 



merely in proximity to the genital pore came to be com- 

 pletely fused with the edges of the latter opening which consequently 

 became the oviducal aperture. 



URINOGENITAL CONNEXION. We have already summarized for 

 the Aiiiphili;i the course of development of the urinogenital network 

 the system of tubes or vasa efferentia which connect testis and 

 kidney and which serve as the outlet for the sperrn. It is now 

 necessary to glance at some points in the general morphology of 

 this system of tubes. It has already been indicated that at their 

 genital end the tubes become merged together in the axial cavity of 

 the testis. The latter we must regard as morphologically an isolated 

 portion of splanchnocoele into which the spermatozoa are shed although 

 it is no longer traceable to splanchnocoele in actual ontogeny. It has 

 also been suggested that the tubular channels were probably 

 originally open grooves of the peritoneal lining which became con- 

 verted into closed tubes as the gonad became isolated from the 

 main splanchnocoele. 



The vasa efferentia frequently show a tendency, more or less 

 pronounced, to anastomose together into a network. In the 

 Amphibia it is a very general though not invariable rule that 

 anastomosis takes place close to the edge of the kidney, forming the 

 longitudinal " marginal canal " which is conspicuous in most 

 Amphibians. A similar marginal canal is formed in Elasmobranchs. 



In taking a general view of the system of vasa efferentia we find 

 that one of its characteristics is, as in the case of the gonad itself, a 

 tendency to increased localization of its functional portions. Thus 

 during ontogeny in Amphibians the vasa efferentia towards the 

 hinder end of the series become blocked and non-functional, or dis- 

 appear entirely, leaving only those at the anterior end functional. 

 This process reaches its limit in such forms as Alytes or Discoglossus 

 where only two or a single member of the series persist. 



Similarly in Elasmobranchs the number of functional vasa 

 efferentia becomes reduced to a few at the anterior end of the series 

 (Centroplwrux 9, Scyllium 6, Acanthias 4-6, Pristiurus 3, Mustelus 

 2-3, Raia 1). The same happens in Amniota. 



In the Dipnoi on the other hand the localization takes place at 

 the hind end of the series, the functional vasa efferentia being 

 reduced to about half-a-dozen (Lepidosiren) or to a single one 

 (Protopterus). 



Another phenomenon which makes its appearance is the simplifica- 

 tion and shortening of the route by which the spermatozoa pass from 

 the vasa effereutia towards the exterior. Primitively the vas efferens 

 opens into an otherwise normal Malpighian body containing its 

 glomerulus and continued into a functional renal tubule. This 

 condition may persist (Rana esculenta, Bufci), or the glomerulus may 

 disappear (K temporaria), or finally the whole Malpighian body and 

 its tubule may be shortened and widened and converted into a simple 

 tubular continuation of the vas efferens towards the opisthonephric 



