1905. ] PLACENTA OF THE SPINY MOUSE. 287 
large efferent vessels which presumably debouch into two maternal 
veins (MV). 
These large efferent maternal vessels are more peripheral in 
position than the afferent courses. 
The fcetal blood-supply is less easily followed. The allantoic 
arteries, on reaching the surface of the placenta, radiate and 
subdivide and give off branches which pass into the placenta at 
intervals over the more central part of the surface. These pass 
(as regards the main stream) straight through the fetal half of 
the placenta, but give off at frequent intervals small capillaries, 
which take a more sinuous and radial course, anastomosing, forming 
network, and collecting together again into veins, which I believe 
to run parallel with the arteries of the villus. 
A considerable amount of connective tissue accompanies these 
villi for the first part of their ingress into the placenta. 
Comparison with other Placentas. 
The placenta is clearly of the type which I have described 
elsewhere as cumulate as contrasted with the plicate type 
characteristic of such groups as the Ungulates. 
The general shape, the arrangement of the membranes and 
their character, resemble, according to the interpretation placed 
upon them above, the condition that pertains in J/us musculus, 
and, rather less closely, that of J/ws decumanus. 
Jenkinson has recently given an account of the development of 
the placenta of the Mouse, which differs in several important 
particulars from that of Duval, which, until that time, had been 
generally accepted. 
Jenkinson agrees with Duval as regards the general arrangement 
of membranes and in the main features of the development. 
He differs, however, in respect to the vascular system, and my 
account given above is in complete agreement with Jenkinson. 
I see also nothing to suggest the appearance of an ingrowth of 
the trophoblast into the maternal blood-vessels, and growth along 
the inside as described by Duval (“‘ plasmode endovasculaire ”). 
Another point of disagreement is with reference to the 
glycogenous tissue. Duval takes but little notice of this and does 
not seem to have found the maternal glycogenous mass, which, 
according to Jenkinson, degenerates, and the space occupied by it 
becomes subsequently filled with a second glycogenous tissue 
which is of foetal (trophoblastic) origin. 
This is a matter of very considerable interest. It is not to be 
expected that an isolated case in an allied genus can afford any 
conclusive evidence. 
Unfortunately the method of preservation (corrosive sublimate) 
is not suitable to the study of glycogen. 
Tested with iodine I find no trace of glycogen, but there are 
certain spaces in the trophoblast cells alluded to in the foregoing 
