418 
existing knowledge of the subject on which they have undertaken to 
write, when we compare it with the summary which they offer on 
p. 253 of No. 138 of this journal and the appended remark »A cela se ‘ 
bornaient nos connaissances sur la distribution de l’hémoglobine dans 
le grand groupe des Invertebrés, quand, en 1873 etc.« 
London, May 1883. 
3. Upon the Foetal Membranes of the Marsupials. 
By Henry F. Osborn, Asst. Prof. of Nat. Science, Princeton College, N.J., U.S.A. 
I have recently been making a study of the foetal Membranes of 
the Marsupials which has brought out some new facts in regard to the 
early life history of these animals. I send you an abstract of my re- 
sults which will be published in full in the July or October number of 
the Quarterly Journal of Microscopical Science. 
My material for examination consisted (1) of a large number of 
Opossum embryos, which were found in the uterus of a recently impreg- 
nated female, (2) a foetus, considerably advanced, which was obtained 
from one of the smaller Australian Marsupials, (3) a Kangaroo foetus 
of about twelve days intra-uterine growth. The relations of the mem- 
branes in all these embryos were found to be very much as in the Kan- 
garoo foetus described by Professor Owen in 1833. Each embryo was 
surrounded by a large subzonal membrane. Within this the embryo 
lay closely enveloped in the amnion. The yolk sac, supplied by two 
arteries and a vein, was very large and had a disclike area of attach- 
ment over about one third of the inner surface of the subzonal mem- 
brane. This attached area was in most cases circumscribed by the, 
vena terminalis of the yolk sac and was highly vascular. The Allan- 
tois was found in all stages of development, in the Opossum and Kan- 
garoo it was free, in specimen 2. it was slightly adherent to the sub- 
zonal membrane without any signs of villi. 
In the Opossum embryos, which were the first observed, the sub- 
zonal membrane over the attached portion of the yolk sac was found 
to be covered with conical villi just visible to the naked eye. Under 
the microscope these were found to be hollow upgrowths of the sub- 
zonal epithelium consisting of a single layer of columnar cells. The 
subsequent relations of these villi could only be conjectured, but in 
specimen 2 similar villi were found composed of a cap of flattened 
subzonal cells covering asolid papilla formed upon the 
surface of the yolk sac. The latter was supplied with capillary 
blood vessels so that in all respects these yolk sac villi may be con- 
sidered similar in structure with the simplest type of allantoie villi 
