48 A. A. W. HUBRECHT. 
by the letters Pp. (protochordal plate) and Pw. (proto- 
chordal wedge). Brauer’s figure leaves not the least doubt 
that the cells indicated by Pp. are of entodermal, and the 
cells Pw. of ectodermal origin, nor do his own views on this 
point differ from mine as he calls the former “ vegetative,” 
the latter ‘animale Zellen.” 
The later transformation of this henceforth fused region 
of double proliferation (see Figs. 85 and 86), fused on 
entirely the same plan as was noted not only in Tarsius but 
in very numerous other mammals, will be discussed later on. 
We must first look out for the third centre of proliferation. 
And we find this in Brauer’s fig. 59, here copied in Fig. 86 
where at a short distance behind the protochordal wedge 
and separated from it by an interval comparable to what we 
notice in the Tarsius, Figs. 46 and 48 (where the interval is 
at its minimum), the ectoderm is seen’ to undergo a new and 
very marked proliferation, which will give rise to tissues 
closely corresponding to the ventral mesoblast which we saw 
origimating in this spot in mammals. 
The difference between the case of Tarsius and Hypogeo- 
phis is this, that in the former this posterior centre of 
proliferation is conspicuous first of all, whereas in the latter 
the two other centres have precedence. However, in this 
respect the other mammals side with the Amphibia, the 
protochordal plate and wedge being visible before or arising 
simultaneously with the proliferating centre for the ventral 
mesoblast. 
Having thus established well-founded comparisons between 
Brauer’s figures of early Gymnophiones (Ceecilia) and our 
own for mammals, we will now turn to the Anura, and take 
as starting-point Brachet’s figures (’03) of the frog. 
In his earlier publication of the year 1903 (Figs. 6, 7, 39—47) 
we find that Brachet describes early stages both for the 
Axolotl and for the frog in which the presence of a proto- 
chordal plate can hardly be denied by any impartial observer, 
One of his figures, copied here in Fig. 79, leaves little 
doubt about the presence in the entoderm of the frog ofa 
