EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 23 
A second author in whose investigations a reptilian plas- 
moditrophoblast has come to light is Schauinsland (?03). In 
his figures of the young Chameleo (Fig. 76) and Sphenodon- 
embryo (Fig. 77), we notice that the rising folds of ectoderm, 
which are the first indications of the separate existence of 
amnion and serosa, are covered, externally, by a layer of 
varying thickness. ‘lhe presence of this layer seems to me 
indicative of a similar process in reptiles as was noticed 
in mammals, viz. a differentiation of the region outside of the 
ectodermal shield (as such we encounter the trophoblast 
after the embryonic ectoderm has been interpolated in it) 
into a superficial and a deeper layer (plasmodi- and cyto- 
trophoblast of v. Beneden and Hubrecht). And this differen- 
tiation arouses suspicion, further confirmed by the sharp dis- 
tinction at the free border of the amnion fold between outer 
and inner layer (Figs. 76 and 77, that. in reptiles the case may 
stand as in bats (Fig. 8a), and in the hedgehog (Fig. 38) 
where the outer surface of the amnion-fold is trophoblastic, 
whereas the inner is an upgrowth of the ectodermal shield 
(see also p. 77) and Duval (99, figs. 96, 102 and 117). The 
trophoblast of Sphenodon and Chameeleo would thus be more 
than one cell thick even before the somatic mesoderm has 
made a diplotrophoblast of it. This trophoblast does not con- 
tribute to line the inner surface of the amnion cavity. Here 
only the embryonic ectoderm (see pp. 76—78) comes into play. 
In this important respect Schauinsland thus sides, although 
not himself discussing the merits of the problem (which was 
not before his mind), with Mitsukuri and not with Mehnert. 
In Chameleon of which Schauinsland gives good illustrations 
(03, Pl. 26, figs. 184—186), which are very indifferently 
reproduced in Hertwig I, 2, p. 194, the same phenomenon is 
observed with quite as much distinctness (Fig. 76). After 
the amnion has closed in the very primitive fashion charac- 
teristic for Chameleon (Fig. 75) the ‘‘ membrana serosa”’ 
consists of a double layer of trophoblast (Fig. 76). 
desirable, from the very first, to keep an open eye for all the different possi- 
bilities that may help to elucidate these difficult points. 
