400 A. A. W. HUBRECHT. 
accumulation other preparations than the one here figured give definite 
evidence. With reference to the nuclear and chromatic elements here figured 
in the trophoblast, the same remark applies that was made with respect to 
the histological detail of the embryo figured on the preceding Plate. Fig. 8 
gives less detail, but perhaps a clearer appreciation of the number of cells 
that contribute towards the formation of the trophoblast, an embryo in this 
stage. (Mus. Utr. Cat. n® Erin. 146 a’, 2 r. 2s.) 
PLATE XXIII. 
Fie. 40.—A section through the same region of Figs. 37—39 in a still further 
advanced stage of development. The embryo is not visible in this figure, 
because the section has passed tangentially just outside the embryonic vesicle, 
the central space (sp.) thus directly bathing the embryonic trophoblast, as can be 
shown by comparing the next section in the series. The small round corpuscles 
in this and the following figures are maternal blood-corpuscles. The relation 
of the space (sp.) to the embryo can be still better ascertained by a glance at 
Fig. 41. A section just outside the embryo, vertical to the surface of the 
paper, would here have the same aspect. c. Blood-vessels in the decidua that 
are closely contiguous to the embryo, and are characterised by a very marked 
and proliferating endothelium, irregular and partly confluent spaces being 
thus called forth in the immediate vicinity of the embryo and communicating 
with the spaces (sp.) in the trophoblast. D. The decidual stroma. g/. Re- 
mains of tubular gland. ¢. Epithelium of uterine recess (inner epithelial 
surface of decidua reflexa). coa. Coagulum, partly filling this recess before 
the final coalescence of the lips. There is a cloudy space to the right of the 
bottom of the recess, which is on three sides surrounded by proliferating 
endothelium cells. This appears to be a remnant of disintegrating uterine 
glandular tissue. (Mus. Utr. Cat. n° Erin. 147 », 4 s-) 
Fie. 41.—Similar section through the embryo and the region in which it is 
embedded at a slightly older stage. D. and ce. as in Fig. 40. Ay. The hypo- 
blast. Zr. The trophoblast of the tangentially-cut embryo. sp. The spaces 
in the outer wall of the trophoblast, widened out simultaneously with the 
stretching of the trophoblast and communicating with the blood-spaces (¢.). 
Ty. s. Cellular tissue which is formed by the accumulation of the cellular 
derivates of the endothelial proliferation in the blood-cavities immediately 
surrounding the embryo. This lacunar, spongeous, cellular tissue, soaked 
with maternal blood, which, through it, penetrates into the lacune (sp.) of the 
trophoblast, was called the trophospongia. Together with the trophoblast 
it may be said to constitute the trophosphere. (Mus. Utr. Cat. n% Erin. 
147 ¢, 4r. 7 8.) 
Fic. 42.—Fragment of a section through the surface of the blastocyst and 
its surroundings, in a stage which is again somewhat further advanced. Letters 
as in the preceding figure. (The trophospongia has increased in thickness, 
