52 A. A. W. HUBRECHT. 
inaugurated are phenomena of gastrulation, instead of phe- 
nomena of notogenesis, that consequently all conclusions were 
naturally biassed. However, the mammalia have come to 
show us the way out of the labyrinth and a reformation of 
our views must be the consequence. 
Without for the present entering into further details 
concerning protochordal plate, protochordal wedge and their 
derivates in the frog, we will now see whether the third 
centre of proliferation which we also have recognised in 
Brauer’s Gymnophiones is as clear in the Urodeles and the 
Anura. 
On this point Brachet’s researches, and those of other 
authors afterwards to be cited, leave no doubt whatever. 
The ectodermal centre of proliferation, hitherto known as 
the ventral lip of the blastopore is very clearly marked off 
(Figs. 80—82), and produces its mesoblastic derivates with 
perfect regularity, in a sequence that is immediately com- 
parable to what we have found in and described for the 
mammals. Brachet writes about this third centre (’05, p. 
67) that it is: “‘ Un épaississement notable de la partie toute 
inférieure de Vlectoblaste.’ And further (I. c., p. 68): 
“Meme épaississement considérable de l’ectoblaste qui vient 
par une large base se continuer avec les éléments du bouchon 
vitellin et cela 4 une certaine distance dans la profondeur de 
Poeuf.” 
We have here before us the ventral mesoblast which in 
Tarsius (and the other Primates) arises so uncommonly early 
and stretches round the umbilical vesicle, creating a very 
early segregation of splanchnic as against somatic mesoblast. 
When we take the Figs. 81 and 82 (copied from Brachet) 
we can immediately recognise the homology between the 
region marked vm and that of Figs. 46,48, and 49, to which 
the same lettering is attached. We also see that if the 
mesoblast there produced in the Amphibia were to attain 
the early development it has in Tarsins and the cavity 
enclosed therein, this would similarly take the place of the 
so-called segmentation cavity, and be applied against the 
