WOLFFIAN DUCT AND BODY IN THE CHICK. 17 



chicks of all ages from nine to thirty protovertebrse, have 

 entirely convinced me that the usual statements on this point are 

 not true, and show to my mind most conclusively that the duct 

 and tubules of the Wolffian body in the region in question do 

 develop in continuity, precisely as do the duct and peritoneal 

 openings of the head-kidney in most Ichthyopsidan types. 



The number of rudimentary tubules in each segment of this 

 region I have not determined precisely. They occur as often 

 as not between the segments, and there seems to be about two for 

 each segment. In the seventh segment I have never seen more 

 than one. 



Before proceeding to give an account of the further develop- 

 ment in the next region, I will briefly refer to the points in 

 which my observations differ from those of previous observers 

 on the development of the Wolffian duct. 



Gasser's account^ of the development of the Wolffian duct is 

 the most recent and exact. In his valuable paper will be found 

 a complete account of the literature of the subject, to which 1 

 need not further refer. 



"The first trace of it which he finds is visible in an embryo 

 with eight protovertebrse as a slight projection from the inter- 

 mediate cell mass towards the epiblast in the region of the three 

 hindermost protovertebrge. In the next stage with eleven pro- 

 tovertebrse, the solid rudiment of the duct extends from the 5th 

 to the 11 th protovertebrae ; from the 8th to the 11th 

 protovertebrae it lies between the mesoblast and epiblast, and is 

 quite distinct from both, and Dr. Gasser distinctly states that 

 in its growth backwards from the 8th protovertebrae the 

 Wolffian duct never comes into continuity with the adjacent 

 layers. In the region of the 5th protovertebrag, where the 

 duct, &c., was originally continuous with the mesoblast, it has 

 now become free, but is still attached in the region of the 6th 

 to the 8th. In an embryo with fourteen protovertebrae the 

 duct extends from the 4th to the 14th, and is now free between 

 epiblast and mesoblast for its whole extent." 



The points in which the preceding account diff'ers from that 

 of Dr. Gasser's briefly are : 



1. The position of the continuous ridge of the Wolffian duct. 



2. The subsequent complete isolation of the duct in the 

 region of the ridge. 



3. The independence of the backward growth of the duct in 

 the 12th to the 15th segment. 



I have never seen any trace of the Wolffian duct in front of 

 the 7th segment, and in all the chicks I have examined I find 



* ' Arch, fiir Mic Anat.,' vol. liv. 



