STUDIES IN MAMMALIAN EMBRYOLOGY. 359 
hedgehog may be easily gathered, as also the points of 
difference. I will reserve the discussion of these different 
points of agreement and disagreement till after I shall have 
given due notice to what Frommel has lately laid before us. 
Frommel’s important work on the bat’s placenta has given me 
more especial satisfaction, because of the beautiful and most 
accurate reproductions in his figures of the histological details 
of his preparations. I am thus enabled, though agreeing with 
Duval in differently interpreting Frommel’s preparations, very 
fully to compare the phenomena that obtain in Vespertilio 
murinus with those that are characteristic for the hedgehog. 
Moreover, others that are interested in these questions of the 
histology and phylogeny of the placenta will only have to com- 
pare Frommel’s and my own figures side by side, and can then 
judge for themselves whether or not they agree with me in 
finding numerous and important points of resemblance. 
As it is not my intention to carry out this comparison from 
the earliest steps through all the successive later stages, but 
merely to touch upon the more salient points, I will in the first 
place refer to Frommel’s fig. 21, on Pl. x11. This section 
through the placental area is taken in an early stage of the 
apposition of the allantois against the trophocalyx (as this 
specialized region may conveniently be called, both in the bat 
and the mole, per analogiam with the trophosphere of the hedge- 
hog and the trophodise of the rabbit). There is first an inner- 
most Jayer—the one which Frommel marks D. §. This is 
evidently the protoplasmic nucleated layer, pierced in all 
directions by lacunze with maternal blood, for which van 
Beneden and Duval vindicate a direct origin out of the epiblast 
of the blastocyst. Taking this for granted, the layer directiy 
corresponds to the hedgehog’s trophoblast (77.), as figured in 
Pls. XXIV, 44, and XXV, 54, which is about in the same stage 
and also over-filled with maternal blood-corpuscles. As in the 
hedgehog, we notice in the bat the same remarkable tendency of 
this layer to send forth in the direction towards the embryo 
very numerous centripetal projections, forming ever so many 
highly vascular papille, between which those of the allantois, 
VOL, XXX, PART 3.—NEW SER. AA 
