DEVELOPMENT OF EMBRYO OF FOWL. 



47 



The enumeration of the postbrachial nerves in the sections 

 gives the following results : I to 6 on each side are in front of 

 the leg-rudiments ; the following seven nerves on each side enter 

 the leg-rudiments. On the right side there is only one incom- 

 plete ganglion back of the last leg-nerve, /'. e., the fourteenth 

 postbrachial ; the nerve from this cannot be traced. On the left 

 side there are four complete ganglia and myotomes back of the last 

 leg nerve (14 to 17 postbrachial). Thus, as might be expected, the 

 hind limbs are normal, and the cloacal region is strongly affected. 



FIG. 7. Defective embryo (Experiment 18). 



In the embryo of this experiment the Wolffian ducts have 

 normal relations, but the allantois is thick-walled and undilated ; 

 the entodermal cavity of the latter opens out into a groove in the 

 splanchnopleure, leading back to the hind-gut, which is not 

 closed as it normally is ; in fact in this embryo the cloaca is the 

 only closed region of the hind-gut ; immediately in front of the 

 cloaca it is open ventrally. The stalk of the allantois therefore 

 appears first as a groove on the left side ; followed forwards, this 



