236 
EICHAl^D ASSHETON. 
the “ Teleostean Eggs and Larvfe from the Grambia River,” 
shown how like the conditions are, that is to say physiologi- 
cally, to the mammalian egg, for the Deckschicht is continuous 
with the yolk mass, which is one piece with the hypoblast ; 
but I see no reason to think this is anything but analogy. 
The Deckschicht of the Amphibia is, however, a verv 
different thing. It was to the Deckschicht of Amphibia that 
Hubrecht in his paper (’95) drew attention as being the 
homologue of the trophoblast and amnion of mammals. But 
as he says now, “ I would never look upon the Deckschicht of 
the Amphibia as having been the first starting-point of what 
afterwards becomes amnion and chorion of the higher 
mammals. We may safely say that Deckschicht and tropho- 
blast are homologous and of similar descent, but we cannot at 
present fully picture to ourselves what has been the arrange- 
ment of the larval envelope in the common parent form from 
which both have derived ” (p. 81). 
Again, ‘^the cells of the Deckschicht proclaim their transi- 
tory and larval significance yet further by the fact that they 
disappear in later developmental stages, and that it is only 
with the constitution of peculiar larval organs that they play 
any part ” (p. 80). 
“It should, however, be observed that if we are willing to 
admit the homology of the Amphibian Deckschicht with the 
Mammalian trophoblast, we must then unhesitatingly go one 
step further” (p. 81). Thus, Hubrecht clearly relies chiefly 
upon the assumed homology of the Amphibian Deckschicht 
and Mammalian trophoblast. 
I think I can convince Hubrecht that the Amphibian 
Deckschicht must, like the “ epitrichial layers” of the 
Sanropsids, be rejected as something different from a tropho- 
blast or purely larval envelope. 
If Hubrecht will examine sections of the segmented egg of 
Ran a temporaria, Bufo vulgaris and probably other 
Anura and of larval stages up to 5 or 6 mm., he will find that the 
Deckschicht layer takes a very important part in the forma- 
tion of the tissues of the brain. They become the neuroglia 
