124 



GREGORY. 



[VOL. I. 



have proliferated at the point of union, and to have become 

 more than one cell thick. When this connection with the 

 ectoderm is artificially severed, the appearance of the Anlage 

 and the overlying ectoderm shows that the connection must 

 have been a true fusion. In some cases the Anlage seems to 

 carry away with it a few cells of ectodermal origin. Camera 

 drawings showing these conditions from the two sides of an 



FIG. i. 



FIG. 2. 



embryo are seen in Figs. I and 2. This fusion is, however, of 

 very short duration, and there is no sign of it in later stages. 



The part of the duct receiving the pronephric collecting 

 tubules is developed with the pronephros from this same 

 Anlage, but the origin of the duct proper, vis., that portion 

 which lies beyond the last pronephric tubule, is more difficult 

 to establish. The preparations made showed in all stages a 

 very constant condition of fusion between the tip of thedistally 

 growing duct and the ectoderm. In some cases this fusion 

 extended for a considerable distance, in others over only a few 

 sections, perhaps not more than one or two. There were only 

 one or two exceptions, which could be readily explained by 

 accidental separation or from the short duration of the union. 

 On the other hand, there were cases where the duct existed 

 perfectly free in the space between the somites and the ecto- 



