hall: mesonephkos A^'D mulleeian duct in amphibia. 99 



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

 found the Miillerian duct connected anteriorly with the second evagina- 

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

 secondai'ily. 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 Fllrbringer, or other authors, as necessarily incorrect. 

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

 effereutia in Rana, which had its origin in the fact that the observers 

 were working on different species, we have been taught that it is not 

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

 alike even in the same (jenus. 



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

 tions of Fiirbringer 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 longitudinall}^ to form the 

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

 The splitting begins anteriorly and progresses gradually caudad. Shortly 

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

 the ostium abdominale by fusing with the 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 " lateralwarts neben uud zwisclien den beiden Trichtern " 

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

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

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

 earl}^ separates from the segmental duct to grow back free. Hoffmann 

 was unable to determine whether or not the Wolffian duct remained 

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

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

 tainly completely isolated. The 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 



