EXPLANATION OF FIGURES ON PLATES. 177 



Fig. 102. Section from the region of the sixth mesoblastic 

 somite. 



Fig. 103. Section from the region of the undifferentiated 

 mesoblast fold. 



Figs. 104-111. Transverse sections from an embryo 

 with eight mesoblastic somites. Stage of Figures 

 48, 49. 



Fig. 104. Transverse section from the most anterior end of 

 the body. 



Fig. 105. Succeeding transverse section. 



Fig. 108. Succeeding transverse section through the anterior 

 part of the neuropore. 



Fig. 107. Succeeding section through the posterior part of 

 the neuropore. 



Fig. 108. Succeeding transverse section immediately behind 

 the region of the neuropore. 



Fig. 109. Transverse section through the posterior part of 

 the first mesoblastic somite. 



Fig. 110. Transverse section through the second mesoblastic 

 somite. 



Fig. 111. Part of a transverse section through the fourth 

 mesoblastic somite, considerably enlarged. The notochord is 

 indeed cut off, but still shows a flat ventral canal, which takes 

 its part in the bordering of the cavity of the mesenteron. 



PLATE IX. 



Figs. 112-119. Transverse sections from embryos 

 with 9 mesoblastic somites. Figs. 112-115 belong to 

 one series of sections. Figs. 116-119 to another. 



Fig. 112. Transverse section from the most anterior end of 

 the body, notochord slit still open. 



N 



