394 MINOT. [Vox if 
finds below the chorionic membrane numerous sections of villi; 
if the specimen be a young chorion, —first to third month, — 
the villi are large, with a good deal of room between them ; their 
outlines are very irregular, and there are relatively few small 
branches (Cut 16). The older the specimen, the larger the 
proportion of small branches. 
In an old chorion—seventh to 
ninth month—the number of 
small villi of nearly uniform size 
is very striking (see the figure 
of a section through a placenta 
im sttu, given in Cut 35). 
The abortion of the villi of 
the chorion lave takes place by 
an arrest of development and = 
a subsequent slow degeneration 
of the tissues, which lose all recognizable organization in the pro- 
toplasm, and to a large extent of the nuclei; at the same time 
they alter their shape (Cut 17), becoming more and more filamen- 
tous; by the fourth month only a few tapering threads, with 
very few branches, remain. The villi disappear almost com- 
pletely from the lzve, except near the edge of the placenta, 
where they are to be found, even in the after-birth, imbedded in 
Cut 17. — Aborting villus from a 
chorion of the second month. 
Cut 18.—Section of the chorionic membrane of an embryo of three weeks; 
stained with osmic acid; mes, mesoderm; ect, ectoderm; a, outer, 4, inner layer of 
ectoderm. From a section prepared by Prof. Theodor Langhans. X 445 diams. 
