564 



( 'RESSW ELL 8 H E ARER. 



been unable to follow the fate of the invaginated cells during 

 gastrulation in surface views of the living egg as he was 

 able to do. In the following work I have relied entirely on 

 the evidence of sections. By means of the combined celloidin- 

 pai-afl&n method of embedding, one is able to obtain good 

 sections of small gastrulte such as these. For fixing I hare 

 found sublimate acetic and Flemming solution give satis- 



T EXT- FIG. l!i. 



^tnrt. 



Section of early trochoplioi-e of Eiiponuitus. ca\m. Ccelomeso- 

 blast. inesc. Meseiicbyme. ///. Mouth, sfm. Stomodieum. 



factoi-y results. From these sections I have followed the 

 formation of the gastrula cell by cell. No mistake can be 

 made, therefore, in the position of these cells, as is frequently 

 done in the study of surface views alone, and one does not 

 get flattening and distortion from the pressure of the cover- 

 glass, as is invariably the case in the study of living prepara- 

 tions. The fertilised egg measures about 55 /li in diameter. 

 The eggs laid under normal conditions are almost spherical, 



