l8o Edivin G. Conklin. 



Posterior Half Embryos; 32' Cells to Tadpole Stage. Fixed and Stained Preparations. 



Fig. 53. Posterior half of 32-cell stage, dorsal view. The cleavage is altogether normal. Spurted 

 in the 4-cell stage, fixed i hour later. 



Fig. 54. Posterior half of 76-cell stage {cj. Fig. 6); spurted in the 4-cell stage, fixed 2 hours later. 

 Two rows of yellow crescent cells are present, the inner being mesenchyme, the outer muscle cells; the 

 anterior pair of mesenchyme cells (B*-") are larger than normal. There are two pairs of caudal 

 endoderm cells (B^-' and B^-^). A pair of ventral ectoderm cells is visible in the midline behind. 



Figs. 55-57. Three views of one and the same embryo; spurted in the 4-ceU stage, fixed 4 hours 

 later, normal embryos being in the stage represented by Fig. 11. Fig. 55. Dorsal view of the super- 

 ficial ectoderm. The notch in front represents the notch in the ventral lip of the blastopore. Fig. 56. 

 Same view, deeper focus, showing the muscle cells beneath the ectoderm; these cells are continuous 

 from side to side, there being no chorda in the midline. Fig. 57. Same view, still deeper focus, showing 

 the double row of ventral endoderm cells in the midline, and on each side of this a mass of mesenchyme 

 cells. 



Fig. 58. Ventral view of posterior half embrj'o of the same stage as the preceding, showing the 

 muscle and mesenchyme cells beneath the ectoderm and on each side of the strand of ventral endoderm. 



