176 Edzvin G. Conklin. 



Anterior Half and Three-Quarter Embryos; 76 Cells to Metamorphosis. 



Figs. 47, 48. Anterior-ventral three-quarter embryo of the 76-celI stage (r. Figs. 5 and 6); the 

 dorsal posterior cells B^-', containing all of the yellow crescent, were killed in the 8-cell stage. The 

 ventral ectoderm cells (Fig. 47) are quite normal both in position and number (c/. Figs. 5 and 47); the 

 anterior dorsal cells are also normal, but the posterior dorsal cells (muscle, mesenchyme and caudal 

 endoderm) are entirely lacking, (c/. Figs. 6 and 48.) 



Figs. 49-51. Three views of one and the same anterior half embryo of about the 250-cell stage; 

 spurted in the 4-celI stage and fixed z hours later. Fig. 49. Dorsal view, superficial focus, showing 

 the neural plate. Fig. 50. Dorsal view, deeper focus, showing two rows of chorda cells besides several 

 ectoderm and endoderm cells. Fig. 51. Dorsal view, still deeper focus, showing the cells of the 

 ventral ectoderm. 



Fig. 52. Anterior half embryo, dorsal view. Spurted in the 4-cell stage, fixed 22 hours later. 

 The yellow crescent is plainly visible in the injured cells. Sense spots are present but the neural plate 

 never forms a tube. The chorda cells lie in a heap at the left side. There is no trace of muscle sub- 

 tance or of a tail in this anterior half embryo. This embryo is from the same experiment as Figs. 

 57-40; normal larva? of this stage are undergoing metamorphosis. 



