BKOOKS AND RITTENHOUSE. On Turritopsis. 



PLATE 34. 



The older stages of the development of the embryo. 



Fig. 35-39. Sections of successive stages of development to show the way 

 in which the outlines of the cells gradually disappear until, 

 in the stage that is shown in figure 39, they are converted 

 into a syncytium with no traces of cell boundaries. Mitosis 

 of the cells of the blastoderm in the early stages of segmenta- 

 tion. 



Fig. 40-41. Mitosis of the cells of the blastoderm during the early stages of 

 segmentation. 



Fig. 42-46. Amitotic division of the cells of the blastoderm during the later 

 stages of segmentation. 



Fig. 47. The first traces of the differentiation of the ectoderm. 



Fig. 48. The ectoderm is well defined and there are traces of the differentia- 

 tion of the cells of the endoderm. 



Fig. 49. Section of a planula a little older than the one shown in figure 48. 



