EARLY ONTOGENETIC PHENOMENA IN MAMMALS. a5) 
III. SavrorsipA AND ORNITHODELPHIA. 
As to this class I have no observations of my own to offer. 
But we may glean from the researches hitherto published by 
others the following data which concern the participation of 
the entoderm in the formation of mesenchyme. 
For the sparrow Schauinsland (’03) figures both a surface 
view, a longitudinal and a transverse section which leave no 
doubt about the presence in this bird of a very clearly defined 
protochordal plate, arising as a proliferation in the entoderm 
before any process of mesoblast formation has been inaugurated 
in the ectoderm. I here copy five of his figures (Figs. 105— 
109), adding that the region in the surface view which I have 
termed the protochordal plate is named by Schauinsland the 
“ Hntoblasthof.” Not only is its situation in perfect corre- 
spondence with the same region in Sorex, visible in Figs. 59 
and 60, but the sections reveal the same constitution (Fig. 104 
for the sparrow, Fig. 58 for the shrew), viz. a local thickening 
of the entoderm. And later when the ventral mesoblast (cf. 
p. 39) will have begun to make its appearance the surface 
view of bird and mammal will again be directly comparable, 
and the independent increase of tissues—intricately inter- 
woven though deriving from different germ layers— 
undeniable. 
Similarly in representatives of the reptiles there is no want 
of recent illustrations by various authors, showing that the 
median entodermal proliferation (protochordal plate) is present 
in early stages. I copy some of Passer (Figs. 104, 110), 
five of Sphenodon (Figs. 77, 78, 112—114), and two of 
Chameeleo (Figs. 76, 111), all seven taken from Schauinsland. 
And I may add that Mitsukuri (93), Mehnert (’92, 94), and 
Davenport (796, Pl. VII) have revealed a similar state of 
things for tortoises, Strahl (’82, ’84), Will (’90), and Corning 
(99) for lizards, Voeltzkow (’93) for crocodiles. 
If the presence of a protochordal plate in Sauropsids may 
thus be looked upon as well established we have to look a 
