ORGANS IN THE EMBRYO OF THE FOWL. 123 



" Toutes des observations nous font connaitre le role physiolo- 

 gique de 1'amnios dans la vie embryonnaire. II est bien evident 

 que 1'amnios protege 1'embryon centre toutes les actions meca- 

 niques qui tendraient a le comprimer." 



HULL ZOOLOGICAL LABORATORY, UNIVERSITY OF CHICAGO, 

 April, 1903. 



POSTSCRIPT. 



After the foregoing paper was fully printed, my attention was 

 called to an article by Weldon in which anamniote embryos of 

 the fowl were described, and which I had overlooked owing to 

 the fact that the observations were included in an article entitled 

 "Prof, de Vries on the Origin of Species" (Biomctrika, Vol. 

 I., Part III., April, 1902). Partial or complete suppression 

 of the amnion resulted from experiments to replace the water 

 lost by evaporation in the incubator without preventing the 

 process of evaporation itself. "A hole was made in the broad 

 end of the egg-shell and the subjacent membranes, into which one 

 end of a siphon, filled with water, was fitted. The other end of 

 the siphon was placed in a reservoir of water, and the whole ap- 

 paratus placed in an incubator. In from 20 to 30 per cent, of 

 the embryos treated in this way the amnion was largely or en- 

 tirely absent after incubation for three or four days." 



Weldon does not discuss the mechanics of formation of the 

 amnion, but treats the result simply as an example of a definite 

 relation between the environment and an extremely stable char- 

 acter. Apparently the immediately effective factor in the experi- 

 ments was the increased pressure within the shell, which, pre- 

 sumably, forced the embryonic area into immediate contact with 

 the shell membrane, and thus prevented the uprising of the 



amniotic folds. 



F. R. L. 



