No. 3.] UTERUS AND EMBRYO. 397 
acid (see azte, Cut 18). In Professor Langhans’ preparations 
the cells are all stained much deeper than the matrix; they have 
an elongated form, and run in various directions more or less par- 
allel to the epithelium ecto; hence many of them are cut trans- 
versely or obliquely. Whether the differences noted are due to 
the methods of preparation must be decided by preserving the 
same chorion in part with osmic acid, in part with Miiller’s fluid 
or picrosulphuric acid, the latter being the reagents I have used. 
In specimens of the tenth week, the matrix of the chorionic meso- 
derm has quite altered in character, being no longer homo- 
Cut 1g. — Section of the chorionic membrane of an ovum supposed to belong to 
the third week; ec¢, ectoderm; es, mesoderm; a, outer, 4, inner layer of ectoderm; 
stained with alum-cochineal. * 445 diams. 
geneous, and at the same time it has increased in thickness. 
For the most part the matrix stains lightly, and where it is 
lighter it contains fibrils of extreme fineness, and running curly 
courses ; there are also streaks of lightly stained matrix, giving 
the impression of fibres resulting from portions of the primitive 
colorable matrix being left. In other parts of the layer the 
primitive matrix is still present, and we find a homogeneous 
well-colored basal substance, the cell lacunae of which appear 
light by contrast, as in Cut 19. One can distinguish also the 
