370 A. A. W. HUBRECHT. 
tions. He recognises that the facts that are furnished by a 
study of the rabbit’s placentation give little help in obtaining 
light as to some of the changes in the human uterus, the 
differences being too great. I will not enter upon Minot’s in- 
vestigation of the rabbit, but will merely note that his inter- 
pretations do not coincide with those of Masius and Duval, 
although, with respect to the point which in this memoir has 
come more especially into the foreground, the trophoblastic 
proliferation, he remarks with due reserve (1. ¢., p. 877) : 
‘ Outgrowths of the chorion penetrate the glandular layer 
of the placenta: whether these outgrowths are in the form of 
villi, in the sense that they preserve a covering of foetal 
ectoderm, was not ascertained, although the tips of the out- 
growths appear to have such a covering.” 
Perusal of the later contributions to this subject may perhaps 
lead him to accept Masius’ and Duval’s interpretation, for 
which the hedgehog offers further arguments. 
Minot’s contribution to our knowledge of the human 
placenta, is of very great value, and will enable us in the follow- 
ing chapter to draw comparisons with what was here described 
for more primitive mammals, such as would not have been 
possible without his richly illustrated memoir. To this part 
of his paper I will refer at somewhat greater length. With 
great justice, Minot remarks (l.c., p. 389) that the human 
chorion has been the object of greater misconception than 
perhaps any other organ of the body. In his summary he notes 
the following concerning the chorion : 
“The chorion consists of two layers, mesoderm and ectoderm, 
both of which are present over all parts of the chorion through- 
out the entire period of pregnancy. . . . . The ectoderm 
during the first month divides into two strata, an outer dense 
protoplasmic layer and an inner, less dense, cellular layer.’ 
1 Independently of Minot’s observations, Ed. van Beneden has quite lately 
had occasion to convince himself of the presence of these two layers in the 
human trophoblast (‘C. R.de la Soc. de Biologie,’ ser. 8, t. v, p. 731), which 
he is inclined to compare with the similar differentiation noticed by him in the 
bat. Langhans and Kastschenko have also seen this duplication of the 
external trophoblast in the human subject, 
