Experimental Studies on Germinal Localization. 209 



Normal Development and Larva from Egg-Fragment, Patella; x 200. 



13, 48-cell stage, lower pole: 14, larva of 9 hours, sagittal optical section, 

 division of 3D; 15, larva of 12 hours, optical sagittal section, showing left 

 primary mesoblast (?) in division; 16, the same larva, in frontal optical sec- 

 tion; 17, trochophore of 30 hours, from the left side (from a total preparation, 

 shell-gland (s. g.) and primary mesoblast (m) from a corresponding actual 

 section), prototrochal cells in surface-view, body-wall in section; 18. larva of 

 20 hours, from upper pole, showing the cells as accurately as possible (some 

 of those just anterior to prototroch could not be clearly seen and have been 

 omitted); 19, optical section at the level of the prototroch of normal larva 

 of 24 hours; 20, larva of 24 hours from fertilized egg-fragment that segmented 

 like a whole egg, prototrochal cells in surface-view; 21, optical section of the 

 same larva at the level of the prototroch; in all these figures the prototrochal 

 cells are shown as acurately as possible. 



