ORGANS IN THE EMBRYO OF THE FOWL. 



IO/ 



mesoderm. In places one cannot determine where the ectoderm 

 leaves off and the entoderm begins. 



Anmiotic Rudiments of tlic Left Side. A short distance in 

 front of the margin of the opening there is a sharply defined fold 

 of the somatopleure capped by an ectodermal thickening that 



e.a. 



FIG. 8. Experiment 57. Upper surface of blastoderm, op. , aperture in the blas- 

 toderm made by the operation ; e.t!., amniotic rudiment of the left side ; /./. , tail-fold 

 of the amnion. The stippled area behind the embryo represents an aperture in the 

 blastoderm accidentally made in opening the egg for the operation. 



represents the head-fold and left lateral fold of the amnion. The 

 extent of this fold is indicated by the line e.a. on Fig. 8. It 

 begins as a sharply marked fold at the most anterior angle of 

 the opening, and passes back, at first along the edge of the open- 

 ing, later a short distance from it, to the left of the embryo. It 

 very distinct (Fig. 10, /.<?./".) to the point where it is indicated as 

 is a broken line ; in this region the fold has disappeared, but the 

 thickening of the ectoderm (ectamnion), may be traced back to 

 the tail-fold with which it becomes continuous as indicated in the 

 drawing (Fig. 8). At no place, until the tail-fold is reached, is 

 the somatopleure internal to this line thrown into folds. By 



