^2 . K. MITSUKURI. 



58 (PI. VIL). The head-fold of the embryo is sunk 

 below the level of the blastoderm and enveloping it is 

 the proamnion ns yet only slightly developed. 



DIag. 11 and II'. Corres])ond to Fig. 2 (PI. I.). The 

 aioniotic hood prot'ceding backward has covered the 

 anterior half of the embryo. Its cephalic portion con- 

 sists of the hypoblast and epiblast ; its dorsal portion 

 of the epiblast alone. IT represents a cross-section of 

 the dorsal region. It shows clearly that the mesoblast 

 has as yet no share whatever in any part of the amnion 

 (or more properly proamnion). 



Dwg. Ill and III'. Correspond to Fig. 3. (PI. I.). 

 The amniotic hood has extended nearly to the posterior 

 end of the embryo. The extra-embryonic cœlomic 

 cavities of two sides are nnited across in the head-region. 

 The mesoblastic f )lds have also insinuated themselves 

 into the hitherto solid epiblastic dorsal part of the 

 amnion (HT.) A partition — tJie sno-amniotic couiicc- 

 tion — in the median line, however keeps the cu'lomic 

 cavities of tw(^ sides separate in the dorsal region. 



IJiag. IV and IV'. Represent the stage when the posterior 

 tube of the amnion is fully developed. The sero- 

 amniotic connection in a cross-section (IV'.) is now 

 closely invested on each side by the mesoblastic fold, 

 and is longer than in III'. The mesoblastic fold is 

 peeling the hypoblast otf the proamnion covering the 

 head. (IV.). 



Diag. V. TAH but a small proximal part of the posterior tube 

 has now disappeared. The sero-amniotic connecticm is 

 more developed. The mesoblastic fold has now entirely 



