EXPLANATION OF FIGURES ON PLATES. 179 



Figs. 125-128. Transverse sections of an embryo with 

 11 mesoblastic somites. 



Fig. 125. Transverse section from the middle of the body ; 

 on the right side the section passes through the mesoblastic 

 somite boundary running obliquely, so that hare the cavities of 

 two successive stages are passed through. 



Fig. 126. A succeeding transverse section. 



Fig. 127. Transverse section through the last mesoblastic 

 somite but one. 



Fig. 128. Transverse section through the most posterior, 

 i.e. eleventh, mesoblastic somite. Mesoblastic somite cavities 

 in open communication with the cavity of the mesen- 

 teron. 



Figs. 129-144. Transverse sections of two embryos of 

 similar age, with 14 mesoblastic somites. Figs. 129-136 

 belong to one embryo, Figs. 137-144 to t he other. 



Fig. 129. Transverse section through the anterior opening 

 of the neural canal. The two diverticula of the mesenteron 

 are passed through b.y the section. 



Fig. 130. Succeeding transverse section. The right diver- 

 ticulum is lacking here, but the anterior end of the mesenteron 

 (J) is passed through. 



Fig. 131. Succeeding transverse section. The left diver- 



4 



ticulum also is not more than touched. 



Fig. 132. Transverse section from the region in which the 

 first small opening of the mouth perforates later on. 



Figs. 133 and 134. Transverse sections through the region 

 in which the club-shaped gland is formed. 



Fig. 135. Transverse section from the middle of the bod3 T . 



Fig. 136. Transverse section, where on the left the oblique 

 mesoblastic somite boundary is touched. 



Fig. 137. Transverse section from the posterior quarter of 

 the embryo, twelfth mesoblastic somite. 



