STUDY OF RABBIT BLASTODERMIC VESICLES IN ALCOHOL. 171 



though they may everywhere else, when fresh, be separated from one another, the 

 germ-layers at this point cannot be separated, except by tearing. Finally, in the 

 next stage there grows out in front of Hensen's knot the so-called head-process, an 

 axial band of cells in which the notochordal canal develops. 



A ..-vvv^^^;vip^ 



^>..-i....-^fe''v' :.!'-;'<.;.''* '-<t\ 





B 





^^^ 



.<?' 



v '^vr.;^-^KV : !g;i;:' 



'"" '"'&, 



FIG. 126. THREE TRANSVERSE SECTIONS OF A RABBIT EMBRYO OF SEVEN AND ONE-HALF DAYS. SERIES 622, 



SECTIONS 247, 260, 381. X 300 diams. 



Examination of Cross-sections. The structure of the embryonic shield is well 

 shown by cross-sections. Figure 126 represents three sections through the embryonic 

 shield at seven and one-half days: A, through the head process; B, through Hen- 



