598 



MORGAN AND HAZEN 



^PLANATION OF PLATE XXXIII. 



Figs, i-io, except Figs. i,A and 7 A, were drawn with Zeiss 4, oil immersion 

 2 mm. Figs. i,A and 7 A were drawn with Zeiss 4 D. The figures in the plate 

 were reduced one-third. 



The material from which the figures (except Fig. 6) were drawn was killed in 

 Flemming's solution, the stronger formula. Fig. -6 was drawn from material killed 

 in Hermann's fluid. The section from which Figs. 7 A, B, C, D, and Figs. 9 

 and 10 were drawn was stained in iron haematoxylin. The remaining figures 

 were drawn from unstained material. 



Fig. I. Sagittal section of an embryo at midnight. There is an artificial 

 rupture in the ectoderm ; d., dorsal ; v., ventral. 



Fig. 2. Sagittal section of an embryo at 2 a.m. 



Fig. 3. Sagittal section of an embryo at 4 a.m. 



Fig. 4 A. Oblique section of an embryo at 5 a.m. 



Fig. 4 B. Enlarged drawing of area marked x'va. i, A. 



Fig. 5. Sagittal section of an embryo at 6 a.m. 



Fig. 6. Part of a cross-section through the posterior third of an embryo at 

 8 A.M. 



Fig. 7 A. Sagittal section through an embryo at 11 a.m. 



Fig. 7 B. Enlarged dra^\•ing of area marked x in y A. 



Fig. 7 C. Enlarged drawing of area marked j in 7 A. 



Fig. 7 D. Enlarged drawing of area marked z in 7 A. 



Fig. 8. Drawn from the anterior region of a longitudinal section of an 

 embryo with eight body cavities ; eci., ectoderm ; end., endoderm ; i.e., body cavity. 



Fig. 9. From the anterior wall of an embryo, showing a portion of a cell 

 after division. 



Fig. 10. Dividing cell from the endoderm of Fig. 16. 



