ORGANS IN THE EMBRYO OF THE FOWL. 119 



which a complete amnion has been found without any tail-fold. 

 These embryos, are, however, defective at the hind end, so that 



FIG. 18. Experiment 18. The embryo 48 hours after the operation. The tail- 

 fold of the amnion has not regenerated. The amnion ends with a free edge in front 

 of the hind-limbs. A fold of blastoderm is wrapped around the embryo and amnion. 

 Under surface of blastoderm. 



one has not to attribute any work of supererogation to the ante- 

 rior lateral folds to explain the complete closure. This also will 

 be discussed elsewhere. 



GENERAL DISCUSSION. 



The formation of the amnion of the chick seems to be a proc- 

 ess with extraordinarily slight power of regulation. 1 A slight 

 injury to part of its early rudiment sets the whole process astray. 

 It is thus an extremely good example of correlative differentia- 



1 Barfurth ('02) notes incidentally in one of his experiments " die Amnion war 

 regenerirt." As I understand him, he means by this simply that an aperture made 

 in the amnion in the course of an experiment on the eye closed up. I can confirm 

 this from my own observations. I have found that even considerable tears made in 

 the amnion after its formation may close completely. 



