HUBRECHT. Pt. P. 
pp 80 nch 
UM 
Um 
Fig. 78. Another transverse section of Sphenodon (after Schauinsland, ’03) 
to show the differentiation of the twolayered trophoblast tr as against the ecto- 
dermal shield ZZ‘; pf protochordal plate. — Fig. 79 to 82. Four longitudinal 
sections of frog-embryos (after Brachet, ‘02). In Fig. 79 protochordal plate / 
and protochordal wedge pw have become differentiated; in Fig. 80 the noto- 
chord (xch) is further developed and the ventral mesoblast 7 makes its appea- 
rance; in Fig. 81 the segmentation cavity has coalesced with the enteric cavity 
that has become visible during notogenesis; in Fig. $2 notochord, somites and 
gut are formed, headfold has’ become visible, ventral mesoblast 2 developes 
below and behind the entoderm cells 
