154 MARY J. GUTHRIE AND HOPE HIBBARD. 



EXPLANATION OF PLATE III. 



FIG. 13. Section through a i6-celled stage passing through the short axis 

 of the group of micromeres. 



FIG. 14. Section through a i6-cellcd stage passing through the long axis of 

 the group of micromeres. 



FIG. 15. Section of slightly older stage showing multiplication of micromeres. 



FIGS, i A<J, i6b, i6c. Serial sections of an older embryo showing migration of 

 micromeres. 



FIGS. 170, 17^, ijc. Serial sections of a still older embryo showing further 

 migration of micromeres. 



FIGS. i8a, iSb. Two of a series of sections showing more numerous mesen- 

 chyme cell- (micromeres). 



