SPOLIA NEMORIS, 105 
and Hensen.' The rabbit and the bat were more especially 
employed in these researches; Heape has added the mole, 
Selenka several other rodents as well as the opossum, whereas 
the hedgehog and the shrew were studied by myself. Of late 
Duval and also Robinson have again investigated the rat and 
the mouse. Nevertheless, we are at present very far from a 
consensus of opinion as to the significance and the genesis of 
the parts in the early didermic mammalian blastocyst. 
In his well-known paper on the early development of the 
rabbit, Ed. van Beneden was one of the first to give a com- 
plete set of valuable illustrations of the segmentation of the 
mammalian ovum and of the consecutive stages between that 
process and the didermic blastocyst in which the mesoblast 
begins to make its first appearance. 
Several of his figures have since passed into every text-book, 
although his interpretation, both of the earliest and of the later 
stages, is not adhered to in the form in which it was originally 
given. Concerning the earlier stages, Lieberkithn (I. c.) and 
afterwards Kolliker* have demonstrated that not only the lower 
layers, but also the epiblast of the embryo arises out of the 
inner cell-mass—v. Beneden’s “ masse endodermique.” Con- 
cerning the later stages, they pointed out that van Beneden 
mistook (l.c., pl. 5, fig. 7, and pl. 7, fig. 2) for the mesoblast 
what is in reality the embryonic epiblast. The latter mistake 
was due to the presence of a trophoblastic layer of flattened 
cells outside that embryonic epiblast. 
As to the development of the hypoblast, van Beneden made 
out that both in the rabbit and the bat it gradually extends 
centrifugally around the inner surface of the monodermic 
blastocyst, the centre of this irradiation being the thicker knob 
of tissue where the embryo is being shaped. 
Similar formation of the hypoblast has been described by 
1 “ Beobachtungen iiber die Befruchtung und Entwickelung der Kaninchen 
und Meerschweinchen,” ‘ Archiv f. Anatomie und Entwickelungsgeschichte,’ 
Bd. i, 1876. 
2 “ Die Entwickelung der Keimblatter des Kaninchens,” ‘ Zoolog. Anzeiger,’ 
iil, 1880, pp. 370 and 390. 
