SECOND PERIOD OF DEVELOPMENT. 61 



particularly that so far as my observation went the 

 axis drawn from the upper to the lower pole crosses 

 the longitudinal axis at an acute angle. 



In profile we see what is afterwards the anterior 

 end indicated by a place that is more sharply curved, 

 which in relation to the upper pole, occupying as it 

 does the middle of the curve, lies excentrically, so 

 that the greater part of the curvature belongs to the 

 ventral side, the shorter section to the dorsal side. 



The understanding of the stages, in which follows 

 the closing of the gastrula-mouth, presents difficulties, 

 especially in reference to their mutual position. I 

 will now describe the changes of form quite ob- 

 jectively, and without attempting any explanation. 

 In the first place during the diminution of the gas- 

 trula-mouth the flat cap-formed stage takes a deeper, 

 as it were, hemispherical form (Fig. 26). The bilateral 

 symmetry finds its strongest expression in the flatten- 

 ing of that side which corresponds to the later dorsal 

 side. In the progressive diminution of the gastrula- 

 mouth the embryo gradually takes a form which, on 

 the front view, has nearly a circular outline, and in 

 profile causes the flattening of the dorsal side to be 

 more and more strongly expressed (Figs. 29-32). The 



