KIDNEY IN RELATION TO WOLFFIAN BODY IN THE CHICK. 151 
it is hardly necessary to say anything about 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’JPO- 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, t. 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. 3. 
In fig. 2 we have what practically amounts to a continuation 
of the body-cavity into the intermediate cell mass (^ 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 protovertebrso. 
VOL. XX. NEW SER. 
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