EARLY ONTOGENETIC PHENOMENA IN MAMMALS. Dal 
the embryonic ectoderm come to the surface, has become 
indistinct. It was above shown how perfectly distinct this 
is in monodelphian and didelphian mammals, and how there 
can be no doubt of its occurrence in Ornithodelphia (Fig. 
70). Still this latter group helps us to explain how it was 
that it became indistinct and thus unrecognised in Sauropsids. 
An outer trophoblastic layer has been described by 
Mehnert (94, p. 214), who perfectly recognised its identity 
with the layer for which in Mammalia I had introduced the 
name of trophoblast, but who has created confusion by 
nevertheless proposing the new name of teloderm! (Grenz- 
blatt), and greater confusion yet by comparing heterogenous 
cell-layers as I will yet further indicate. Mehnert describes 
in detail how in the embryo of Emys lutaria the outer germ 
layer becomes didermic and produces two layers that are 
totally different from each other, of which the deeper layer 
furnishes the material for the definite epithelium of the 
tortoise and represents the primitive epidermis, whereas the 
outer layer of flattened cells, the trophoblast (Mehnert’s telo- 
derm), should be looked upon as a supra-epithelial layer. 
According to Mehnert the trophoblast can be quite easily 
separated from the epiderm (I. c., p. 213, Pl. IX, Fig. 8). 
The growth of the trophoblast is said to be dissociated from 
that of the deeper epithelial layer. Mehnert claims to have 
established (on the authority of Mitsukuri’s [’93] figures) 
the presence of a trophoblast in Clemmys japonica and in 
‘rionyx japonica, in Lacerta muralis, Tropidonotus, and for 
birds in the duck, the chick, Larus, Sterna, Podiceps, Buteo, 
Aegialitis, Hirundo, Luscinia, and others. Now I must begin 
1 The reason he gives for substituting a new name and not applying the 
name of trophoblast is, ‘that it has not been proved that those cells partici- 
pate in the first place towards the nutritive processes of the embryo.” In this 
he is in full contradiction to Schauinsland (03, p. 83) who holds it to be 
“sehr wahrscheinlich” that these very cells have a nutritive significance in 
reptiles. In the Mammalia, where the layer is ever so much more con- 
spicuous, its phagocytic significance has been proved; but even if it had not, 
this seems hardly to justify Mehnert for over-burdening scientific nomencla- 
ture by the creation of a superfluous synonym. 
