SEAL-EMBRYOS. 19 
In most of the recorded cases the uterus contained but a single foetus, as is the 
case in the uterine specimens in this collection. Mayer, quoted by Turner, records an 
instance in Phoca vitulina in which the left horn of the uterus contained five embryos 
and the right horn four. Turner also had in his possession twin foetuses from the 
uterus of a Phoca greenlandica. There can, however, be no doubt that the presence 
of more than a single foetus is quite exceptional, and that the foetus is situated in 
one or other of the cornua, the non-gravid horn being very slightly, if at all enlarged. 
There is little or nothing to add to the description already given by Turner of 
the macroscopic characters of the placenta. As is the case in the Carnivora generally 
the placenta of the seal is zonary» The fcetal surface (fig. 16) shows a series of 
elongated cord-like elevations with intervening depressions. These elevations lie more 
or less parallel with one another and run in the long axis of the placenta itself (fig. 16). 
The histological characters were examined by means of longitudinal and transverse 
sections from the margin and central portion of placenta of different ages. In order 
that no point of importance should be overlooked I submitted the sections for 
examination to my friend Mr. Richard Assheton, who has done so much to elucidate 
the structure and comparative anatomy of that organ, and to his kindness I am 
indebted for the description here given. 
Two distinct stages are represented in the specimens examined. The earlier one 
is of an age equivalent to the 24th to 26th day of pregnancy of the dog, the older of 
an age equivalent to perhaps the 40th to 45th day of pregnancy of the same animal. 
There is, as one would expect from Turner’s description (10), a very close resemblance 
to the placenta of Carnivora such as the dog or ferret. 
In the earlier stage the angioplasmode formation of Duval has become well 
established but forms as yet only a thin layer. The mouths of the uterine glands are 
blocked by the trophoblast and by degenerated uterine epithelium, but the preservation 
of the material is not sufficiently good to determine the boundary between the two. 
The distal parts of the glands are expanded, and by this expansion and consequent 
thinning out of the intervening tissue the “ lamelles mésentériques ” are formed (fig. 17). 
In the younger stage the embryonic blood corpuscles are still nucleated. Even 
in the early stages lacune containing extravasated maternal blood, lying between the 
maternal tissue and the trophoblast—or bounded on nearly all sides by the trophoblast 
—have commenced to appear. (Compare Assheton 1, pl. 13, Canis.) 
In the older specimen (fig. 18) the angioplasmode layer has increased enormously. 
In the earlier stage it is only about one-sixth to one-quarter of the thickness of the 
sub-mucous layer, whereas in the later stage it is about twice the thickness of that 
layer. The dilated glands are now still more dilated, and Mr. Assheton thinks that in 
many cases the angioplasmode projects into their cavities. 
The lacunz of extravasated maternal blood are large and the trophoblast cells 
forming their walls are gorged with red maternal blood corpuscles. 
There appear to be no important differences between the placenta of the seal and 
D2 
