KIDNEY IN RELATION TO WOLFFIAN BODY IN THE CHICK. 67 



it is hardly necessary to say anything ahout it. It is a 

 mass of cells^ (woodcut, fig. 1), stretching between the proto- 

 vertebra (P. v.) and the dorsal inner angle of the body- 

 cavity (p-p.)' It is on its first formation continuous with 

 the peritoneal epithelium. Its relation to the protovertebra 

 is obscure, and I have been unable, so far, to make it out 

 satisfactorily. There is one point, however, to be borne 

 in mind concerning this intermediate cell mass ; it is con- 

 tinuous, i. e. is not divided by the lines of segmentation 

 into areas corresponding to each protovertebra. 



Very soon after the intermediate cell mass is established 

 it undergoes a change. It becomes at some points more dis- 

 tinctly continuous with the peritoneal epithelium, at others 

 less so. And finally this culminates in a clear continuity, as 

 seen in fig. 2, and a marked discontinuity, as seen in fig. S. 

 In fig. 2 we have what practically amounts to a continuation 

 of the body-cavity into the intermediate cell mass {i c m.) ; 

 in fig. 3, on the other hand, the intermediate cell mass is 

 distinctly disconnected with the peritoneal epithelium, and 

 lies as a mass of cells between it and the protovertebra. Al- 

 though these figures are not taken from contiguous sections, 

 fig. 2 being taken from the thirtieth segment, and fig. 3 from 

 the twenty-ninth, yet for all the important details fig. 3 

 represents exactly a section next or next but one to fig. 2. 

 The intermediate cell mass is then now present as a cord of 

 cells continuous from segment to segment, and continuous 

 at intervals with the peritoneal epithelium. Fig. 4 repre- 

 sents the two conditions of the intermediate cell mass, as 

 seen in a single section taken from the twenty-sixth seg- 

 ment. 



At the next stage of development the intermediate cell 

 mass entirely breaks away from the peritoneal epithelium, 

 and lies as a cellular blastema just internal to the Wolffian 

 duct. It may be called the Wolffian blastema. 



The Wolffian blastema almost directly breaks up into the 

 structures constituting the first rudiments of the Wolffian 

 tubules (fig. 5). 



The development of the Wolffian blastema in the chick 

 needs further description. 



In the anterior region of the Wolffian body, as far back as 

 the nineteenth or twentieth segments, the above description 

 of the conversion of the intermediate cell mass into the 



^ The term intermediate cell mass in this account is only used to in- 

 dicate the cell mass connecting a protovertebra with the peritoneal epi- 

 thelium, and never refers to the cell mass occupying the same position 

 before segmentation has given rise to protovertebrse. 



