44 



all. Ou tlie left side, a mere truce of the boundary groove (/>. 7.) 

 is seen. As tlie plane of the section is inclined toward tliat 

 side, the groove is not met with on the right side. The macro- 

 meric field shows no tendency to invaginate. The disturbed part 

 of the cell-mass is found in this section also, x 80. 



F'kj. 27 — An oblique transverse section through the blastoporic depression 

 of an ovum of a stage intermediate between those represented 

 in Fig. 8a and Fig. la, A shallow depression on the macromeric 

 margin {l>p.) shows tlie ventral part of the blastoporic funnel cut 

 through. The archenteron (ar.en.) is roofed by the irregular 

 macromeric epithelium (onac.ep.). An irregular row of macro- 

 meres on either side of and apparently continuous with the roof, 

 (l.mac.ep.) represents the lateral irregular epithelium, x 80. 



pip^ 28 — A more dorsal section from the same series as that just 

 described. The blastopore is represented by a deep notch (h^).). 

 Lateral lips formed by the micromeric layer border the notch, 

 this condition being brought about in consequence of complete 

 withdrawal of the macromeres. x 80. 



j'T'/ry, 29 — A still more dorsal section from the same series, passing through 

 the dorsal lip of the blastopore. The micromeric epithelium 

 {i.mic.ep.) is reflected to form the archenteric roof, while the 

 depressed macromeric field which has been withdrawn represents 

 the archenteric floor. As the section is an oblique one, the 

 anterior part of the archenteron is cut through lengthwise to some 

 extent (the upper part of the figure), x 80. 



Fig. 30 — A horizontal section through an ovum a little younger than tl>e 

 stage represented in Fig. 10a. In the anterior part (the left 

 ])art in the figure), the section passes through the dorsal blastoporic 

 lip. The archenteric roof {i.mic.ej).) is cut througli obliquely, 

 while the posterior part (the right part in the figure) shows in 

 section the ventral part beyond the anterior end of the 



archenteron. Thi^ lateral irregular epithelium (/. mac. ep.) is 

 seen as a continuous laver. x 80. 



