L' 



Plate III. 



'^. 43. Formation of first ectoniere-qnartot. Apical view. 



g. 44. Samo stage, Eight side view. 



g. 45. Formation of second ectomere-qnartet. A[)ica] view. 



g. 4G. Same stage. Posterior view. 



g. 47. Same stage. Left side view. 



g. 4S. Simultaneous formation of third and i'oiirth eetoinere-((nart<'ts sfagxv^. 



Apical view, 

 g. 49. Same stage. Posterior vie\v. 

 g. 50. Same stage. Optical sagittal section, 

 g. .51. Formation of rifth ectomere-qnartet stage. A[»ical view, 

 g. 52. Same stage. ( )ptical transverse section, 

 g. 53. Cleavage oi sixth ectomere-qnartet, and formation of bilateral cells. 



Optical horizontal section. 

 g. 54. Same stage, with formation of seventh ectomere-qnartet, and 



entomere-cell D,. Sagittal section. 

 g. ~)5. Same stage, with formation of hilateral cells. Horizontal section. 

 g. .~)G. Cleavage of mesomere-cell. ( )ptical horizontal section, 

 g. 57. Formation of first entoderm-cells. 0|itical horizontal section, 

 g. 58. Completion of same stage. Optical transverse sectitm. 



59. Stage liefore formation of mesoderm-cell »?, showing the arrangement 



of cells. Cells on ventral side are colored l)lne. 

 (iO. Formation of first mesod(M'm-cell stage. 0[itical horizontal section. 



