58 A. A. W. HUBRECHT. 
they have contributed to Hertwig’s ‘ Handbuch of Embryo- 
logy. The student of their article will find no difficulty in 
accepting the generalisation above arrived at, that the ento- 
derm is the mother tissue from whence the vascular tissue 
and the blood have taken their origin. 
Riickert writes concerning Gecko (lI. ¢., p. 1172) : “Ich traf 
auf eine deutliche Ablésung der hier ziemlich dotterreichen 
ersten Gefissanlagen von dem angrenzenden hohen und 
ebenfalls dottergefiillten Entoblast ... Ihre entodermale 
Entstehung leet daher klar zu Tage.” 
Besides the protochordal plate and the annular zone of the 
entoderm from whence mesenchyme is produced we also find 
in the Sauropsida the ectodermal centres of mesoblast forma- 
tion which we have noticed in the mammals. 
The protochordal wedge is to some extent more marked 
than we found it in the Mammaha; it has of late been 
designated by O. Hertwig (?06) by the name of ‘ Mesoderm- 
sickchen,’”’ and it contains a cavity more spacious than the 
comparatively thin canal which we have encountered in 
mammals (Fig. 98). Also in this respect the exceptional 
ease of Fig. 52 should be considered as throwing a side-light 
on these intricate processes both in mammals and Saurop- 
sids. 
The confluence between the earliest ectodermal downgrowth 
with the protochordal plate has up to now not been specially 
examined in reptiles. Still we may conclude from the figures 
here given, which I copy from other authors that it comes 
about in exactly the same way as we noticed it in Tarsius for 
mammals, and in Hypogeophis for Amphibians. Fig. 419, 
Hertwig (’06), shows us the earliest protochordal wedge in a 
snake as it fuses with the thickened entoderm; behind the 
protochordal wedge we notice the ventral mesoblast as a third 
focus of mesoblast formation. Figs. 427 and 429 are con- 
tinuations of the same in somewhat later phases, and the 
correspondence with our Figs. 79, 80, 97, and 98, of Amphi- 
bians and Mammals is self-evident. In Hertwig’s Fig. 429 
the source of ventral mesoblast has actually been shifted 
