30 A. A. W. HUBRECHT. 
IT need not here enter into a detailed exposition of this 
controversy, now that it has been so carefully done in the 
chapter just mentioned on “die erste Entstehung der 
Gefisse und des Blutes bei Wirbeltieren,” in Hertwig’s 
‘ Manual.’ 
But I will pass on to a full description of what has already 
been observed and described in different mammals commenc- 
ing with what, in 1890, I have called— 
a. The Protochordal Plate.—This structure has at 
first been more or less ignored by many embryologists, later 
its significance has been recognised, but it has then been 
designated by a different name (Bonnet, 01, E.P.); this 
time I hope to establish definitely that [ was not only justified 
to distinguish this protochordal plate as an independent 
anterior source of mesoblast in mammals, but that we ought 
henceforth to admit its presence under varied aspects also in 
Sauropsids and Ichthyopsids, as I will point out hereafter. 
For mammals we have in the preceding paragraph described 
how in the didermic stage the entoderm cells under the ecto- 
dermal shield are considerably more massive than those that 
clothe the inner surface of the trophoblast, the latter being 
flattened and further apart. Figs. 8a, 14, 18, 30, 31 and 36 
testify to this. As the didermic blastocyst increases in size 
there is a very marked phenomenon of further increase 
coupled with proliferating growth in that portion of the ento- 
derm that lies under what will later be the anterior portion of 
the embryonic shield. I here re-figure this for Sorex after 
my own (Figs. 58, 59) for the sheep and dog, after Bonnet’s 
(Figs. 91, 92) publications, and I add new figures indicating 
the same phenomenon in Tarsius (Figs. 48, 49, 50 and 51) 
Galeopithecus (Figs. 18,42). For the pig it has been figured, 
although not viewed in this light, by Keibel (’93, figs. 21— 
23). 
1 Keibel interprets his figures differently, and did not, in the paper above 
referred to, recognise the protochordal plate as a source of mesoblast, such as 
I had defined it three years before. Still the figures here cited leave no doubt 
of its existence in the pig. 
