DA A; A. W. HUBRECHT,. 
the “epiblastic or outer layer of mesoblast of primitive 
streak.” This investigation thus authorises a direct com- 
parison of the phenomena figured in Figs. 101 and 102 for 
Tarsius, in which we have quite decisively recognised an 
epiblastic and a hypoblastic layer of mesoblast of the 
primitive streak, which is what was noticed in the frog by 
Robinson and Assheton. 
It should yet be added that the annular zone of mesen- 
chyme-producing entoderm may in the frog even commence 
as an unpaired ventral sheet, which only later becomes 
paired, and thus more or less annular. Brachet (’03, p. 686) 
expresses this as follows: “Il existe une phase du développe- 
ment ot les cellules vasculaires des futurs vaisseaux vitellins 
forment une couche continue impaire et médiane (Fig. 22) et 
la parité définitive est secondaire.” 
We have now seen that in the three subdivisions of the 
Amphibia we notice early processes of ectodermal and ento- 
dermal proliferation, which allow of direct comparison with 
what we have described for the Mammalia. And we may 
add that the continuity between the derivates of the proto- 
chordal plate and those of the annular zone is in Amphibia 
established even perhaps earlier yet, whereas the continuity 
of these latter derivates with those mesoblastic elements that 
originated right and left of the median dorsal line is again so 
very early established, that it cannot be wondered at that 
the Amphibia have not suggested to previous investigators 
the relative independence of these different sources from 
whence cells and tissues that will take their places between 
the two primary germ-layers arise. 
When we will later recapitulate what are the further lines 
of development of the products of the four proliferations 
above enumerated, the complete homology between Amphibia 
and Mammals will become yet more evident. 
