DEVELOPMENT OF EMBRYO OF FOWL. 



45 



Fig. 6 gives two views of the embryo. The hind end is en- 

 tirely absent, and the opening is filled by the enlarged Wolffian 

 ducts. The band of tissue between the two ducts is the hind end 

 of the alimentary tract. The right side is seen to be less de- 

 veloped than the left. In the view from the opposite side, it can 

 be seen that there is a rudiment of the hind-limb on the left side ; 

 but apparently none on the right. 



This embryo was cut into transverse sections. Study of these 

 shows that there are eight postbrachial ganglia on each side, 

 though the eighth on the right side is smaller than on the left. 



FIG. 6. Two views of a defective embryo (experiment 74). A, amnion ; /, 

 strip of intestinal epithelium; L, leg; IV. D., Wolffian duct. The vitelline blood 

 vessels are somewhat abnormal. 



On the left side the seventh and eighth postbrachial nerves enter 

 the rudiment of the hind limb. On the right side there is no 

 such rudiment, and the seventh and eighth nerves, which are 

 quite large, end bluntly in the mesenchyme, almost as though 

 cut off. The question arises why there is no limb rudiment on 

 the right side ? One can explain this by assuming that the 

 operation destroyed the seventh and eighth postbrachial meso- 



