204 
PROGRESS OF MICROSCOPICAL SCIENCE. 
early stages of these two closely allied species. Although the corre- 
sponding stages agree so closely in form and structure, they are from 
the first readily distinguishable by well-marked specific differences in 
the form and armature of the appendages. In fact, the differences appear 
greater in the larval stages than in the adults. Dr. Stars was not able 
to trace the development beyond the third stage, which he had at first 
supposed could not be the last stage of the larva, but after compa- 
rison with the latter stage of the American lobster, he regards it as 
quite probably the last true larval stage. 
Comparative Anatomy of the Placenta. — Professor Turner, F.E.S., 
who has been lecturing on this subject before the Royal College of 
Surgeons, devoted his second lecture to a consideration of the changes 
which occur in the uterine mucous membrane during pregnancy. He 
pointed out that as soon as the ovum was received into the uterus the 
mucous membrane swelled. The epithelium often, though not always, 
loses its columnar form, and the cells multiply in order to cover the 
increased surface. The subepithelial tissue increases enormously, which 
is due to the multiplication and development of the corpuscles already 
stated to be abundantly distributed through its tissue. The tubular 
branched glands are separated to a much greater distance from each 
other in consequence of the growth of the subepithelial tissue. They 
are augmented in size. The whole membrane becomes much more 
vascular. On its surface pit-like depressions may be seen, which were 
formerly thought to be the enlarged mouths of the glands, but which 
the Professor himself had ascertained to be new-formed pits or crypts 
in the interglandular tissue. The relation of these pits he next pro- 
ceeded carefully to describe, taking the diffused form of placenta of 
the pig, which is the simplest form of placenta, as an example. 
When the mucous membrane of the pig is examined after the entry 
of the ovum, it was found to present a series of folds, which, however, 
like the rug* of the stomach, are only preparatory to its great subse- 
quent dilatation, since they disappear in the distended state. On ex- 
amination with a hand lens fine furrows are seen, which correspond to 
the ridges on the chorion. Also a series of spots corresponding to the 
spots of the chorion ; these spots are feebly vascular. Between these 
are a number of crypts, which are highly vascular. The glands in 
the pig are tubular and much branched ; they open upon circumscribed 
areas free from crypts ; and hence, which is a very important point, 
there is no relation between the glands and the crypts. The crypts 
are lined by columnar and probably by ciliated columnar epithelium. 
The villi of the chorion are received into the crypts, and not into the 
mouths of the glands. The secretion of the glands is not brought into 
direct relation with the villi of the foetus. 
In the mare the mucous membrane is also thrown into folds, and 
there are here also polygonal areas with intervening ridges. Each 
area presents a pattern formed by numerous crypts ; the walls of the 
crypts are highly vascular, the ridges between the collections of crypts 
are but feebly vascular ; the glands here, again, do not open into the 
crypts, but irregularly upon the ridges ; the crypts, therefore, as in 
the pig, which receive the villi, are interglandular, and are not the 
