DEVELOPMENT OF EMBRYO OF FOWL. 4! 



the operation. In the resulting embryo, the trachea is a long 

 tube, the lungs are budding out, the oesophagus is well formed, 

 and the stomach is in two divisions, in the anterior of which the 

 glands have begun to form, and the intestine is slightly coiled 

 and opens on the hind surface, across which it is continued as a 

 superficial strip ending in a free blind tag with a slight lumen 

 (Figs. 2 C and 3). The liver and pancreas are normally formed. 

 In fact the parts present are apparently in the same condition that 

 they would have been had the embryo been intact. 



The allantois is entirely absent ; and there is no evidence of any 

 compensating groivth of the intestine. 



Nervous System. The spinal cord ends bluntly, but the neural 

 canal is prolonged backwards at its ventral angle into a short 

 process which tapers into a bundle of neurites that may be fol- 

 lowed a short distance, and then terminates abruptly. It would 

 appear that the descending tracts in the cord have caused the 

 prolongation, and have then pushed out into the adjacent tissues. 

 A similar prolongation appears in all embryos defective at the 

 hind-end (Fig. 3, AJ. 



Excretory System. - - The Wolffian ducts are much dilated, as 

 there is no outlet for the secretion of the mesonephros (Fig. 3). 

 No metanephric outgrowths have arisen from them, although in 

 the normal embyro of this stage these are well developed. The 

 metanephric region of the Wolffian ducts was of course destroyed 

 by the operation ; but, as the ducts are continuous structures, one 

 would not anticipate that the capacity for producing metanephric 

 outgrowths would be limited to a short stretch at the posterior 

 end. Of course another explanation of their absence than that 

 of limitation of potency to a short region of the Wolffian duct is 

 possible, i. e., that suitable predisposing external conditions for 

 their formation are strictly limited (e. g., that their development de- 

 pends on a certain amount or kind of development of the allantois 



or cloaca). 



Experiment 93. 



In this experiment a very considerable portion of the hind-end 

 was cauterized and removed (see operation diagram). Seventy- 

 two hours later the egg was reopened and found living. The 

 vascular area covered about three fifths of the yolk ; the circula- 

 tion was very active, and there was no allantois. 



