nee 
EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 49 
particular spot of thickened entoderm situated at the very 
place where we would expect the protochordal plate at this 
earlier stage. His other figures, which are also copied here 
(Figs. 80—82) show the subsequent stages. 
And as to the annular band of entoderm from which the 
blood-vessels and blood originate, we find it similarly dis- 
posed in the Amphibia according to Brachet, who for the 
frog writes (03, p. 686), “les endotheliums vasculaires y 
compris |’endothelium endocardiaque et les futures cellules 
rouges du sang, procedent de la portion du mésoblaste 
: qui s’est séparée par délamination de la partie ventrale 
de l’endoblaste gastruléen.” And further (’03, p. 688), “‘ de 
tout le vaste manchon mésoblastique qui se délamine a la 
surface de l’endoblaste gastruléen, la partie ventrale, sur une 
largeur plus ou moins grande selon les régions, se sépare 
complétement du reste 4 des stades relativement peu avancés, 
et, poursuivant dés lors une évolution spéciale, donne nais- 
sance a tout lappareil vasculaire sanguin (endotheliums 
vasculaires et cellules rouges du sang).” 
The term manchon (muff) used by Brachet shows that he, 
too, has observed the region of the entoderm which produces 
the mesenchyme out of which the blood-vessels and the blood 
are developed in the shape of an annular peripheral invest- 
ment of the region out of which the mediodorsal organs will 
develop. 
With most laudable prudence Brachet does not generalise 
his results concerning the frog, but states expressly that for 
Triton he is inclined to stick to the conclusion he arrived at 
already in an earlier publication (’98), and according to which 
also in Triton the vascular system is of entodermic origin, 
but that he all the same thinks a further confirmation of his 
observations desirable, whereas for Axolotl he makes all 
reserves, the study of the origin of the vascular cells being 
here very difficult. He is careful to add, however, that he 
cannot exclude the possibility that after all Axolotl may 
prove to fit into the same plan as the two others. 
Other authors who, before Brachet, have come to similar 
VOL. 53, PART 1.—NEW SERIES. 4, 
