101 



30 mm. are in their second, tliose measuring circ. 50 mm. in their 

 third jear, whilst they become mature in Ihe end of the fourth year. 



The gonads of the immature frogs were taken from the body, 

 together with the kidjiey ; they were tixed in Bouin's solution and 

 after 5 days they were transferied to ale. 90 7o- Subsequently the 

 testes were cut — mostly frontally, but in a few cases transversely 

 — into complete series of sections of 10 ft. The sections were 

 generally stained with Dklafielu's hematoxylin and van Gieson's 

 solution, sometimes eosin or nigrosin was nsed instead of van Gieson's 

 solution. Especially with van Gieson's solution the connective tissue 

 between the seminifei'ons tubules assumes a deep red colour. 



From the testes of the adult frogs only the middle part was 

 sectioned, from all other testes complete series of sections were made. 

 As far as necessary, the sections were drawn on transparent paper 

 at a magnification of 100, with the aid of the large projection- 

 apparatus of Zeiss. ^) By laying these transparent papers on each 

 other, it is generally not difficult to trace the course of the tubules, 

 which are cut transversely. Originally 1 had the intention to project 

 on a certain plane several tubules, passing over into the rete testis 

 with a common stem, but in many cases this method proved not 

 practicable, especially in adult testes, as here the tubules are too 

 close to each other and too much twisted. Fig. 10 is even so 

 schematized that only the mutual relations of the tubules, drawn in 

 one plane, are shown. In order to get an exact insight into the 

 course of the seminiferous tubules a few sections of the part of the 

 testis, in which these tubules occur, are also reproduced. 



In the following the development and structure of the testis tubules 

 ai*e described in the first place and further the particular course of 

 the vasa etferentia in six immature testes is treated. 



T li e development and s t )• u c t u r e of the seminiferous 



tubules. 



An extensive literature deals with the development of the gonads of 

 frog-embryos. As most of these investigations do not bear upon my 

 subject, I will only communicate the results of Witschi, who in his 

 ,,Experimentelle Untersuchungen liber die Entwicklungsgeschichte 

 der Keimdjüsen von Rana temporaria ' (1914) not only traced the 

 different developmental stages of the gonad, but also drew attention 



^) 1 have to thank Prof. A. J. P. van den Bkoek, whose kindness enabled me 



to use the apparatus of the Anatomical Institution of the University at Utrecht. 



7* 



