HALL: MESONEPHEOS AND MULLERLVN DUCT IN AMPHIBIA. 99 



blindly in front, as it sometimes does in Amblystoma, and if he later 

 found the Mlillerian duct connected anteriorly with the second evagina- 

 tion, the impression would be natural that the ostium was formed 

 secondarily. That he found no evagination at that early stage may be 

 due to the fact that the first evagination degenerated before the second 

 was formed — although I have never observed such a condition in 

 Amblystoma. Or, it would be very easy to mistake the first evagination 

 for a nephrostome. It must not be tliought, however, that I criticise 

 the observations of Flirbringer, or other authors, as necessarily incorrect. 

 Since a certain controversy in regard to the development of the vasa 

 efi;erentia in Rana, which had its origin in the fact that the obsei'vers 

 w^ere working on different species, we have been taught tliat it is not 

 safe to take for granted that the details of embryonic development are 

 alike even in the same genus. 



In general Hoffmann ('86) confirms for Triton cristatus the observa- 

 tions of Flirbringer on Salamandra. After reaching the height of its 

 development, the pronephros migrates to a more median and dorsal 

 position and the two nephrostomes draw nearer together. The glomus, 

 which originally occupied a position between the two nephrostomes, is 

 brought to lie opposite the first. About the time when the gills begin 

 to degenerate, the segmental duct splits longitudinally to form the 

 Wolffian duct (dorso-median) and the Mlillerian duct (ventro-lateral). 

 The splitting begins anteriorly and progresses gradually caudad. Shortly 

 after the first appearance of the Miillerian duct its anterior end forms 

 the ostium abdominale by fusing with tlie thickened peritoneal epithe- 

 lium, — generally lateral to, and on a level with, or just posterior to, 

 the second nephrostome, sometimes between the two. This thickening, 

 which is formed by the cells of the peritoneum taking on the columnar 

 shape, existed " lateral warts neben und zwischen den beiden Trichtern " 

 before the appearance of the IMlillerian duct. The backward growth of 

 the duct is different in the two sexes. In the female its whole length is 

 formed by evagination from the segmental duct. In the male it very 

 early separates from the segmental duct to grow back free. Hoffmann 

 was unable to determine whether or not the Wolflfian duct remained 

 connected for a short time with the pronephros after the formation of 

 the Mlillerian duct. Shortly after that event, the pronephros is cer- 

 tainly completely isolated. Tlie ostium is at first quite shallow. The 

 surrounding thickened peritoneal epithelium shares in its enlargement. 



With the formation of the ostium, the degeneration of the pronephros 

 begins. The first steps are the closure of the first nephrostome and the 



