2/2,8 



FIG. 45- SAGITTAL (MEDIAN - LONGITUDINAL) SECTION OF AN 

 EMBRYO OF 26 HOURS. (After Duval.) 



A, anterior end of head. C.I/, medullary canal. EC, endothelium of heart. 

 RE, limit of head-fold, ex, ectoderm. z, entoderm. PC, pericardium. /%, 

 pharynx or fore-gut. Ki, fore-brain, b, mesoderm. 



133 



