PLATE 1 



EXPLANATION OF FIGURES 



3 to 5 Photomicrographs of transverse sections througli the head of the em- 

 bryo in figm-e 1. b., brain; I., lentoids; m., mouth cavity; L., lens; p., plasma in 

 oedematous pericardium; r.L, retinal lentoid; o.s., dissociated optic cup sub- 

 stance, X 150. 



364 



