82 A. A. W. HUBRECHT. 
trace in Amphioxus, the Cyclostomes, and the Elasmobranchs, 
that the deep significance hitherto attached to the foetal 
membranes as a means of subdividing the vertebrates into 
the primary groups of Amniota and Anamnia runs great risks 
of losing much of its significance. | 
We have seen that the name Amniota, as against Anamnia, 
was not well chosen if we consider, as I have advocated, that 
not the amnion, but the chorion, is the primary foetal mem- 
brane, and that the name of Choriata, as against Achoria 
would even have been better; that of Allantoidea as against 
Anallantoidea being yet more defective, as we will see later 
on. 
But now, considering that the chorion is only a derivate of 
the early larval envelope that we have called the trophoblast, 
and that of a trophoblast traces are met with among Am- 
phibia, Dipnoi, Ganoids, and Teleostomes in general, the 
more important division should not come to he, as is at 
present the case, between the Sauropsida on one side and the 
Amphibia on the other, but between those vertebrates in 
which a larval envelope, or traces of it, are found and those 
in which such traces are absent. 
We have seen, by the example of birds and reptiles, that it 
is not always easy to detect traces of the trophoblast, which 
for various reasons is not always quite as distinct as it is m 
mammals. And so even when among vertebrates we have 
descended downwards as far as the Hlasmobranchs and the 
Cyclostomes, the possibility of last traces of trophoblast and 
Deckschicht having been obliterated cannot be denied. Still, 
on quite different arguments supplied by comparative ana- 
tomy, we must recognise that the line here drawn seems 
to correspond with certain distinctive characters of primary 
importance. 
So within the realm of the last-named classes the pheno- 
menon of ossification is wholly unknown. On the other 
hand, the ossification, as it has manifested itself in bony fishes, 
calling forth such bony pieces as the hyomandibular, the 
quadrate, the different pterygoids, the palatina, the maxillary 
