Plate IV. 



Living Eggs of Cynthia partita ; Fourth Cleavage to Gastrula. 



Fig. 37. Sixteeu-cell stage viewed from vegetal pole. 



Fig. 38. Sixteen-cell stage, from the animal pole, yellow protoplasm around the nuclei. 



Fig. 39. Twenty-two cell stage, from the vegetal pole; four mesoderm cells (yellow), ten endoderm, 



chorda and neural plate cells (gray) and eight ectoderm cells (clear). 

 Fig. 40. Same stage viewed from the posterior pole. 



Fig. 41. Egg passing into the 32-cell stage; postero-dorsal (vegetal pole) view. 

 Fig. 42. Thirty-two-cell stage, postero-dorsal view. 

 Fig. 43. Forty-four- cell stage; posterior view, showing separation of mesenchyme (m'ch) from muscle 



cells (ms.). 

 Fig. 44. Same stage, dorsal view, showing subdivision of endoderm cells. 

 Fig. 45. Similar stage, posterior view, showing separation of another mesenchyme cell from a muscle 



cell. 

 Fig. 4(j. Seventy-four cell stage, dorsal view, showing division of 4 chorda and 4 neural piatc cells; 



there are 10 mesenchyme and 6 muscle cells, besides 10 endoderm cells. 

 Fig. 47. One hundred and sixteen cell-stage, showing the beginning of gastrulation, also the neural 



plate, chorda, muscle and mesenchyme cells. 

 Fig. 48. Slightly older stage showing advancing gastrulation with inrolling of cells at edge of blastopore. 



