EAELY ONTOGENETIC PHENOMENA IN MAMMALS. 249 
with, of course, the hypoblast from which these parts are 
derived, together with the epiblast which overlies them, as 
well as everything ventral to the annular zone, constitute the 
protogenetic tissues, which are of more ancient origin than 
the primitive streak tissues, and everything this secondary 
area of proliferation gives rise to (deutei’Ogenesis) are of a 
more recent origin, and include the protochordal wedge of 
Hubrecht (Kopffortsatz of others), the so-called ventral 
mesoblast and the lateral plates of mesoblast which are 
really one and the same thing. 
I entirely agree with Hubrecht’s comparison of these areas 
in question with corresponding ones in Amphibia, pp. 46-54, 
though I claim to be not included among' those who were so 
^‘naturally biassed” as to fail to see these points in Amphibia 
(vide H^uart. Journ. Micr. Sci.,’ vol. 37, PI. 24, figs. 8-11, 
13, 14). 
I have also indicated in the figure herewith reproduced 
from a paper in the ^ Guy’s Hospital Keports,’ 1907, the 
respective regions formed by the protogenetic and deutero- 
genetic centres in various groups of vertebrates, though in 
these I have omitted details such as the annular zone of 
mesenchyme producing hypoblast, which is all included in 
the general white area marked with black dots, but the 
essential features are unmistakably indicated. 
Hubrecht (p. 55) refers to birds and reptiles, and has no 
difficulty in finding evidence in them as in the Amphibia of 
the truth of the presence of two great embryonic growth 
centres in a vertebrate (protogenesis and deuterogenesis), and 
finds the same parts, protochordal plate and annular zone, 
protochordal wedge and ventral mesoblast. 
I am inclined to doubt, from my own observations on the 
sparrow, whether the well-marked mass of cells which occurs 
in the sparrow at an early stage between hypoblast and epi- 
blast, shown so clearly in Schauinsland’s figures and called 
by Hubrecht “ protochordal plate,” is really the material from 
which any of the notochord is formed. If followed it is found 
to gradually take up a more and more forward position, and 
