282 OBSERVATIONS ON THE DEVELOPMENT OF 
embryonic conditions of existing 7e/eoste?, they ought to be all strictly 
homocercal, for it is only in the embryonic state that a Teleostean is 
really homocercal. 
On the other hand, however, if homocercality and heterocercality 
are left out of the question, there can be no doubt that such facts 
as those brought forward by Heckel respecting the Pycnodonts show 
that in certain families of fish, at any rate, there has been a gradual 
change from a quasi-embryonic condition of the vertebral column to 
one more resembling that of an adult Teleostean. So perhaps it may 
be admitted that the structure of the tail in some modern Ganoids is 
more like that of the adult Ze/eoszez, while that which obtains in the 
ancient members of the same group is more like that of embryonic 
Teleoster. But it has never yet been shown, either that the approxi- 
mation of a Ganoid to a Teleostean, or the more complete ossification 
of the vertebral column in these or other fishes, is a mark of an 
advance in general organization. I take this occasion of repeating 
an opinion I have often expressed, that no known fact justifies us 
in concluding that the members of any given order of animals 
present, at the present day, an organization in essential respects more 
perfect (in whatever sense that word may be used) than that which 
they had in the earliest period of which we have any record of their 
existence. 
It may be asked, in conclusion, whether the peculiar structure 
of the tail of the Teleostean tribes is a modification of the vertebral 
column altogether peculiar to them, or whether some trace of it 
is not to be found in other Vertebrata. 1 believe the latter question 
may be answered affirmatively, and that just where so many 
remnants of piscine characters are found, viz, in the Amphzbza, 
there is a most interesting representation of this structure. I refer 
to the coccygeal style of the Frog and its allies, which, as Dugés 
originally indicated (and I have had reason lately to satisfy myself 
of the fact), is formed by the coalescence of a styliform ossification 
of the end of the sheath of the chorda with two neural arches. 
Naturally, as there are no fin-rays, there are no epiural or hypural 
apophyses, but otherwise the resemblance of the two structures is 
complete. 
