14 ADAM SEDGWICK. 



is not, however, complete ; but the Wolffian duct remains connected 

 to the peritoneal epithelium at certain intervals hy short cords 

 of cells. 



In a chick with twelve protovertebrse the separation of the 

 Wolffian duct from the intermediate cell mass in the region of the 

 7th to the 11th protovertebrse inclusive is as complete as it ever 

 will be, i.e. it has separated for the greater part of its length, but 

 remains attached to the peritoneal epithelium at certain points, 

 by cords of cells (fig. 2) derived from the cells of the inter- 

 mediate cell mass connecting the rudiment of the Wolffian duct 

 with the peritoneal epithelium. These cords of cells are the 

 commencing Wolffian tubules of the anterior part of the Wolffian 

 body, and are more numerous than the segments in which they 

 are placed. Behind the region of the protovertebree in a chick 

 of this age (twelve protovertebrse), the Wolffian duct has grown 

 back as an irregular cord of cells (fig. 6), independent of the 

 intermediate cell mass, for a short distance, thus repeating the 

 feature of the last and succeeding stages in this particular. In 

 the region of the last (12th) proto vertebra, however, the cord of 

 cells constituting the Wolffian duct at this stage is now con- 

 tinuous with the intermediate cell mass at certain intervals. 

 Comparing the sections through the 12th segment of this stage 

 with those just behind the 11th protovertebra of the previous 

 stage, it is seen that the Wolffian duct has enlarged, and by a 

 dovvngrowth of cells from it, with which probably is connected 

 an upgrowth from the intermediate cell mass, has become in 

 certain places connected with the intermediate cell mass. These 

 secondary connections constitute the commencing tubules of this 

 part of the Wolffian body. 



In a chick with thirteen protovertebrse an advance precisely 

 similar to that characterising the previous stage has taken place, 

 i.e. the Wolffian duct has become connected with the inter- 

 mediate cell mass in the 13th segment (fig. 1), and behind 

 this point is free from adjacent structures. 



In a chick with fourteen or fifteen protovertebrse the process 

 of development remains the same. So that in a chick with 

 fifteen segments the following is the condition of the Wolffian 

 duct : — It extends from the 7th to the 15th segment as a solid 

 cord of cells, connected at intervals with the peritoneal epithe- 

 lium by the commencing Wolffian tubules; behind the 15th 

 segment it extends for a short distance as a free cord. The further 

 development differs from that just recorded in this important 

 particular ; the duct does not become connected with the inter- 

 mediate cell mass of the newly-formed last segment, but remains 

 separate for a considerable interval of time (till towards the end 

 of the third day) from it. In other words, the formation of 



