146 s. H ATT A. 



Plaie XIII. 



Fig. 1. Vortical section tlirongh an egg of the morula-stage. BB x 2 (Zeiss J. 



Fig. '2. Sagittal section through an egg of the oldest monila-stage. BB x 2. 



Fig. i}. Transverse section through the dorsal region of an embryo in wliicli the 



gastrulation is going on. BB x 2. 

 Fig. 4. Sagittal section of an egg after the completion of gastrulation. BB x 2. 

 Figs. 5 and (5. Sagittal sections of an embryo in which the peristomal mesoblast is 



first seen. BB x 2. Fig. 5, a section through tiie median Ihie ; hg. (5 



a section through a plane slightly lateralto the median line. 

 Fig. 7. Median sagittal section througli the hind end of an embryo far older than 



that of the last two figures. BB x 4. 

 Figs. 8-11. Series of selected transverse sections from an embryo of abotit the same 



stage as that of fig. 7. BB x 4. Fig. 11 has been cut through tlie line n b, 



fig. 10 through the line c </, fig. 9 through the linc^ cf, and fig. 8 through 



the line fi h, in the embryo shown in fig. 12. 

 ï'ig. 12. Diagram of a median sagittal section through an embryo of about the 



same age as that of fig. 5, to show the directions of sections represented 



in fiiïs. 8-11. 



Plate XIV. 



Fig. 18. Transverse section through the dorsal region of an embryo a little older 

 tluui that represented hi fig. 7. 



Figs. 14 and 15. Transverse sections from the dorsal regions <>( a little more ad- 

 vanced embryo ; fig. 15 is more posterior than fig. 14. 



Fig. 10. Transverse section from the dorsal region of a still more advaiiced embryo. 



Fig. 17. Transverse section from the dorsal region of a still more advanced embryo. 



Fig. 18. Transverse section from the dorsal region of a much further advanced 

 embryo. 



Fig. 19. Transverse section through the anterior part of an embryo in which tlie 

 head-prominence is ready to protrude. 



