er.J^ 



- Ill 



228 



250 



Fir. 45. — Sagittal (median - longitudinal) section of an 

 EMBRYO OF 26 HOURS. (After Duval.) 



Ay anterior end of head. CM^ medullary canal. EC, endothelium of heart. 

 RE, limit of head-fold, ex, ectoderm, in, entoderm. PC, pericardium. Ph, 

 pharynx or fore-gut. Kr, fore-brain, i, mesoderm. 



133 



