104 



FRANK R. LILLIE. 



folds formed simply by the process of twisting of the embryo. 

 This distinction is of importance in interpreting the results of 

 the experiments. 



Hirota (94) notices the secondary fold on the upper side and 

 says : " It seems to owe its origin to the presence of the sero- 

 amniotic connection. ... It is always on the right side of the 

 connection, and is pushed on towards the left. There takes place 

 no folding before the allantois appears, and the longitudinal ex- 



e.a. 



J. 



FIG. 6. Section of the same embryo as the preceding, 10 sections (150^) in front 

 of Fig. 5. The section passes through the place of fusion of the right and left folds. 

 The secondary fold of the amnion is well shown on the right side. Letters as in 

 Fig. 5- 



tent of the fold depends on the extent of the sero-amniotic con- 

 nection." " Its form and extent are variable." " It is not clear 

 what significance this fold has." "At both extremities of the 

 sero-amniotic connection the amnion is also slightly folded longi- 

 tudinally." 



These secondary folds of the amnion are very transitory ex- 

 cept in two regions : (i) Above the hind end of the heart (apex 

 of ventricle) and continuing a short distance behind it ; (2) in the 

 region immediately in front of the allantois, at 60-70 hours, thus 

 in the neighborhood of the final closure of the amniotic folds. 

 The former are of very constant occurrence and persist a long 

 time (Fig. 3). The latter are relatively slight and inconstant. 

 Hirota is thus mistaken in saying that these folds do not appear 

 until the formation of the allantois. 



The secondary folds in the neighborhood of the heart are 

 always on the upper (right) side ; they first appear at the time 



