on A, Aw. W. HUBRECHT. 
gists to follow Koélliker in his negation of the participation 
of the entoderm towards the production of mesoblast. 
In Tarsius the distinction of the mesenchyme (derived 
from the entoderm) from other mesoblast-cells between the 
two germ layers is hardly feasible even in the earliest stages, 
because here the source of early ectodermic mesoblast at the 
hinder end of the ectodermic shield is in full flow at a very 
early period in consequence of the presence from the very 
outset of mesoblastic tissue, which I have called the ventral 
mesoblast. It formsasac, partly applied against the umbilical 
vesicle from the very first, and encloses an extra embry- 
onic coelomic space, which is thus present at a very much 
earlier moment than in other mammals with the exception of 
man and monkeys. Part of this ventral mesoblast will 
gradually become the connective stalk (Haftstiel, Bauch- 
stiel) by which the embryo will be in vascular connection 
with the placenta, and which will be fully discussed in a 
later chapter. But in this same Tarsius the entodermal 
proliferation above described for Sorex, and which I will 
continue to designate as the protochordal plate is all the 
more evident. It is figured in diagrams 48, 49, 50,and51. The 
entoderm has here become two or three cell-layers thick. 
‘This region corresponds to what will later be the very front 
part of the head of the embryo, before the primordium of the 
heart has yet been folded in under that of the brain. 
As to other mammals I do not dispose of quite as exten- 
sive data as for Sorex and Tarsius, but there is no doubt if 
we also consult the results of other investigators—even of 
those who deny the participation of the entoderm towards 
the formation of mesoblast—that this thickening of the 
entoderm occurs in all mammals. For Hrinaceus, Gymnura, 
Talpa, and Tupaja I possess numerous convincing prepara- 
tions already mentioned above. Also for Manis, Galeopi- 
thecus, Sciurus, Mus, Lepus. Several of these are here 
figured (Figs. 18,37, 42). For the dog Bonnet gives very un- 
mistakable illustrations (01, Figs. 11—13, 31, 32), although 
i\ 
he substitutes the name ‘ Erganzungsplatte” for the older 
