DEVELOPMENT OF EMBRYO OF FOWL. 53 



the notochord extends a short distance back of the neural tube 

 and its end is very protoplasmic ; its further extension in each 

 case is definitely limited by the surface of operation, against which 

 it is pressed (Fig. 5, A). One receives the impression that its 

 growth has been stopped by the mechanical hindrance. 



One does not expect a vertebrate to show axial regeneration 

 of the trunk, but in certain vertebrates the tail may regenerate. 

 What is the condition in the chick embryo? No. 18 is the only 

 case cited in which any of the caudal somites were left uninjured. 

 In this case there was no regeneration, so far as could be judged. 



The very first experiments that I performed on chick embryos 

 were made to determine whether or not the limb-buds might 

 regenerate. The operations were limited to the wing-buds. I 

 found that it was possible to amputate the right one close to the 

 body at a time when its width was equal to or greater than its 

 length, and even later (four or five days); the wound in the amnion 

 might close, and the amputated part remained in the amniotic 

 cavity as evidence of the operation. In the only cases in which 

 the embryo lived for any considerable period after the operation, 

 there was absolutely no sign of regeneration, though the wing- 

 bud of the opposite side increased in bulk several times. 



So far as I know, the only evidence, that the organs of the 

 chick embryo possess any different power of regeneration from 

 those of the adult, consists of the above observations on the noto- 

 chord (tissue regeneration) and of Barfurth and Dragendorff' s 1 

 observation on the regeneration of the lens of the eye from the 

 edge of the optic cup. The last depends on observations on a 

 single case, and in this case the extent of injury to the eye was 

 doubtful. Until the result is confirmed, I believe we are justified 

 in passing it over. 



There would remain, then, the general conclusion, subject only to 

 the qualifications already noted, that the embryo of the chick pos- 

 sesses no greater power of regeneration than the adult, 



2. As to the Somites. Somites always retain their normal 

 numerical value. But the experiments were not adapted to 

 analyze very accurately the numerous problems presented. 



1 Dietrich Barfurth and O. Dragendorft", " Versuche iiber Regeneration des Auges 

 und der Linse beim Huhnerembryo," Anat. Anz., Erganzungsheft zum XXI. Bd., 

 1902. 



