96 FRANK R. LILLIE. 



4. The opening in the egg is closed as follows : A piece of 

 the shell with membrane attached is cut from a corresponding 

 part of another fresh egg, so as to be slightly larger than the 

 opening in the operated egg. This is placed over the opening so 

 as to close it completely ; and the albumen adhering to the mem- 

 brane acts as cement. To ensure perfect closure strips of the 

 egg-membrane are plastered on so as to overlap all edges of the 

 foreign shell. The advantages of this method of closure are 

 that the foreign surfaces are perfectly aseptic if fresh eggs are 

 used, and that the conditions are as nearly like the normal as 

 possible. It is, morover, the simplest and easiest method. This 

 method of closing the opening was first used by Miss Peebles. 1 



III. EXPERIMENTS ON THE AMNION AND THE PRODUCTION OF 

 ANAMNIOTE EMBRYOS IN THE CHICK. 



A. The Normal Development of the Amnion. 



The purpose of this section is to give a brief statement of some 

 facts concerning the formation of the amnion before taking up 

 the analysis of the processes by experiment. This is necessary 

 because the facts are at least partly new, and without knowledge 

 of them the mechanics of formation of the amnion cannot be 

 understood. For a recent review of the literature on the whole 

 subject of the amnion in the Sauropsida, see Schauinsland ('O2a 

 and '02$) ; the latter paper I regret not to have seen. 



In the somatopleure on each side of the axis of an early embryo 

 of the chick three zones may be distinguished on the basis of the 

 subsequent differentiation, (A) for the body-wall ; (^) for the 

 amnion ; (C] for the chorion (serosa) (Fig. i). It is important to 

 trace the origin of the differentiation between the amnion and 

 serosa on the one hand, and amnion and body-wall on the other, 

 for the conditions that determine the development of the amnion 

 must be antecedent to such differentiation. 



i. The Ectamnion. The differentiation of the amniogenous 

 from the choriogenous somatopleure is always preceded by the 

 appearance of a thickening of the ectoderm along the external 

 margin of the former. This thickening, for which I propose the 



1 Rome's Arc/iiv, VII., 1898. 



