No. 3.] UTERUS AND EMBRYO. 393 
greater regularity of configuration. It is hardly necessary 
to describe the intermediate phases that have been exam- 
ined, but it will suffice to describe the form at full term, Cut 15, 
when the branches are long, slender, and less closely set, as well 
as less subdivided, than at earlier stages; they have nodular 
projections, like brapches arrested at the beginning of their de- 
velopment ; there are numerous spots upon the surfaces of the 
villi; microscopical examination shows that these spots are 
proliferation islands, as we may call them, or little thickenings 
of the ectoderm with crowded nuclei. It appears that not all 
the villi change to the slender form; for some villi, having still 
the earlier, thicker form, are found even in the mature placenta, 
a fact already noticed by Jassinsky, 105, 346. These thick villi 
Cut 16.— Section of the chorion at three weeks. a, layer of coagulum; 4, meso- 
derm of chorion; £4, epithelium, also extending over the villi; /z and Vz',; the meso- 
derm, 4, contains a number of blood-vessels, nearly all in transverse section. X 65. 
usually show also a distinct “cellular layer” in their ectoderm, 
a peculiarity to be considered below again. Seiler, 131a, 
has given figures of the villi at various ages, but fails to show 
the characteristic forms. Langhans has observed the altera- 
tion in the villi, 110, 199, and even justly remarks that many 
of the villi in so-called “moulds” are not pathological, as they 
have been frequently considered, but normal young villi. The 
differences in the villi, according to age, are very conspicuous 
in sections. The sections should of course be made so that the 
fragments of the villi will remain 27 sz¢w, imbedding in celloi- 
dine is convenient for this purpose; if this end be attained, one 
