156 A. A. W. HUBRECHT. 
very great extent homologous both in number, in sequence, 
in position, and in development to similar ossifications in the 
Amphibia, the Sauropsids, and the Mammalia. 
Confining ourselves to the comparative osteology of the 
head we may say that the conformity is very suggestive, and 
that, where nobody advocates any direct descent of the land- 
animals from Teleosts, this conformity might certainly plead 
for the possibility of the inverse proposition. 
This proposition to be taken in the sense above alluded to, 
viz. that great attention should be given to the evident 
probability that the return to an aquatic environment may 
have been by polyphyletic lines of descent and at different 
periods of the earth’s history. 
There is no doubt that we must look towards paleontology 
for furnishing us with the arguments that will have decisive 
weight in deciding these delicate questions of phylogeny, for 
which we can never hope to possess arguments derived from 
splanchnological or from developmental sources. 
And we may at all events expect that as more and new 
fossil finds come to increase our knowledge of the palaeozoic 
epoch, some of them will certainly prove to have a bearing on 
the points here in dispute. 
A division of the vertebrates in the superclasses of Cyclos- 
tomata, Chondrophora, and Osteophora might suggest itself, 
Amphioxus remaining yet more isolated in its yep of 
Cephalochordata. 
The Chondrophora would then contain ihe Elasmo- 
branchs, the Osteophora all the other higher verte- 
brates. 
In further subdividing the Osteophora the existent grouping 
into Teleostomi, Dipnoi, Amphibia, Sauropsida and Mammalia 
might remain, although it will have to be carefully considered 
whether the recent, most considerable progress of paleeonto- 
logy will not allow of a more satisfactory reclassification in 
the borderland between Amphibia and Reptilia, now that we 
have reason to believe that the very sharp distinction which 
in later days was upheld between these two according to the 
