74 



THE SECOND DAY. 



[CHAP. 



Fig. 20. 



Transverse Section through the Dorsal Region of an Embryo of 



45 HOURS. 



A. epiblast. B. mesoblast. C. hypoblast consisting 1 of a single row of flat- 

 tened cells. M. c. medullary canal. P. v. protovertebra. W.d. Wolffian 

 duct. S. o. Soniatopleure. S. p. Splanchnopleure. p- V' pleuroperitoneal 



