556 A. A. W. HUBRECHT. 



Fig. 9. — A similar section through an embryo of No. 105, the zona being 

 much folded. 



Mus. Utr. Cat. n"- Sorex 105, 2 n 6 s. 



Figs. 10 and 11. — Section through two other blastocysts belonging to 

 No. 110. Lettering as in the foregoing. 



Mus. Utr. Cat. n<" 5, Sorex 110, 2 r. 8 and 10 s. 



PLATE XXXVII. 



Fig. 12. — An early blastocyst of Sores in situ in the expanded portion 

 of the uterine lumen. The section is transverse to the axis of the uterus. A 

 small swelling was externally visible (see Fig. 20, which represents the same 

 uterus, natural size, as drawn from the spirit specimen), n. e. The uterine 

 epithelium, bl. Cavity of the blastocyst, already adhering by a small portion 

 of its walls against the surfaces of the mucosa. The embryonic shield is seen 

 to occupy the topmost surface, and to be turned towards the anti-mesometrical 

 concavity of the uterine swelling. In this stage the hypoblast forms already 

 a completely closed sac, constituting the inner layer of the didermic vesicular 

 blastocyst. 



Figs. 13 — 15. — Three outline sketches in natural size of the uteri (spirit 

 specimens) from which the embryos were taken, of which sections are figured 

 on this plate. 



Cat. n«^- 2, 65, 52. 



Figs. 16 — 21. — Surface views of the embryonic area reconstructed from 

 the series of sections through the early stages that were obtained from the 

 uteri of the preceding figures. 



These surface views, and similarly all those that are represented on the 

 following plates, were obtained from camera lucida outlines that had been 

 drawn with Zeiss' apochromatic objective 16 mm., oc. 4. They are thus 

 about sixty-two times enlarged. 



The outline given is not that of the blastocyst, but of the embryonic shield 

 on the top of it. 



The cross arrows indicate the exact extent and direction of the sections 

 that are figured on this plate ; the small numbers beside the arrows refer to 

 the figure which represents the section. 



In Figs. 18, 19, and 21 a distinct protochordal plate was present in the 

 hypoblast ; its outline, as underlying the anterior part of the embryonic 

 shield, is indicated by a grey space. 

 In Fig. 20 all the nuclei that are present in the hypoblast below the 

 epiblastic shield have been figured. It is here seen how they are much 

 more closely packed at the anterior end, i. e. iu the region whicii has 

 here been termed the protochordal plate. 



