822 STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 



peculiar granular contents supported in a trabecular work 

 (Plate 39, fig. 54). This discovery first led us to investigate 

 histologically what we, in common with previous observers, had 

 supposed to be the anterior end of the kidneys in the adult, and 

 to shew that they were nothing else but trabecular tissue with 

 cells like that of lymphatic glands. The interruption of the 

 segmental duct at the commencement of this tissue demonstrates 



o 



that if any rudiment of the pronephros still persists, it is quite 

 functionless, in that it is not provided with a duct. 



Ill . Theoretical considerations. 



There are three points in our observations on the urino- 

 genital system which appear to call for special remark. The 

 first of these concerns the structure and fate of the pronephros, 

 the second the nature of the oviduct, and the third the presence 

 of vasa efferentia in the male. 



Although the history we have been able to give of the prone- 

 phros is not complete, we have nevertheless shewn that in most 

 points it is essentially similar to the pronephros of Teleostei. 

 In an early stage we find the pronephros provided with a peri- 

 toneal funnel opening into the body-cavity. At a later stage we 

 find that there is connected with the pronephros on each side, a 

 cavity the pronephric cavity into which a glomerulus projects. 

 This cavity is in communication on the one hand with the lumen 

 of the coiled tube which forms the main mass of the pronephros, 

 and on the other hand with the body-cavity by means of a 

 richly ciliated canal (woodcut, fig. 4, p. 817). 



In Teleostei the pronephros has precisely the same charac- 

 ters, except that the cavity in which the glomerulus is placed is 

 without a peritoneal canal. 



The questions which naturally arise in connection with the 

 pronephros are: (i) what is the origin of the above cavity with 

 its glomerulus ; and (2) what is the meaning of the ciliated canal 

 connecting this cavity with the peritoneal cavity ? 



We have not from our researches been able to answer the 

 first of these questions. In Teleostei, however, the origin of this 



