[CHAP. 



TRANSVERSE SECTION THROUGH THE DORSAL REGION OF AN EMBRYO OF 



45 HOURS. 



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

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

 duct. S. o. Somatopleure. S. p. Splanchnopleure. p. p. pleuroperitoneal 



