HUBRECHT. Pl. Y. 
TG oy PET 
z YG sealed: STs TYp 
74 CEE OOOO Os re 
Os 
Ser Nala orale 
RO als/a4/0? 
Wn P2Si0 
0) 
ot a 
ge 
Core 
Fig. 120. Longitudinal section of Amphioxus (after Legros, ‘0°). Noto- 
genesis has advanced considerably. At * Legros accepts a separation between 
the lower entodermal layer, originated by invagination and the layer to the 
right of « which he accepts on Lwoff’s example as a product of ectodermal 
proliferation. x would then separate: to the left: protochordal plate pf; to the 
right: the protochordal wedge pw, spun out. — Fig. 121, 122 and 123. Three 
longitudinal sections through blastodisks of Pristiurus (after Riickert, “06). In 
the two first gastrulation by delamination has come about; ec ectoderm, ev ento- 
derm; in Fig. 122 the protochordal wedge pw has fused with the entoderm //; 
in Fig. 123 notogenesis has definitely commenced. g¢ incipient gut cavity. 
