HUXLEY, ON THE SKELETON OF FISHES. isi) 
are sometimes remarked between the two lobes never affect 
the disposition of the rays; for even when the caudal fin is 
cut square or rounded, it is not less invariably divided into 
two nearly equal parts, the superior of which is inserted on 
to the superior apophysis of the last vertebra. We may, 
then, regard this disposition as constant among osseous 
fishes, despite the slight inequality which is sometimes ob- 
served between the superior and inferior apophyses, and not- 
withstanding the curvature of the chorda at its posterior 
extremity.” 
M. Vogt then goes on to point out that since, according to 
M. Agassiz’s researches, all fossil fishes before the Jurassic 
epoch had inequilobed or heterocercal tails, while those with 
equilobed or homocercal tails only appeared subsequently, 
there is a parallelism in this respect between the several 
stages of the embryo of such a (Cycloid) fish as a Coregonus, 
and the groups of fishes which have at successive epochs 
peopled the waters of the globe. In his ‘ Recherches sur les 
Poissons fossiles,’ vol. 11, p. 102, the same doctrine is thus 
concisely expressed by M. Agassiz : 
“© On the other hand, there is neither in the actual creation 
nor in anterior epochs, any adult fish belonging to these two 
last orders (Ctenoids and Cycloids) which has the vertebral 
column bent up, and the caudal fin inserted below it; whilst 
this arrangement is characteristic of embryos in a certain 
period of their existence. There is then, as*we have said 
above, a certain analogy, or rather a parallelism, to be es- 
tablished between the embryological development of the 
Cycloids and Ctenoids, and the genetic or paleontological 
development of the whole class.” 
Professor Owen (‘ Lectures on Fishes,’ 1846) describes the 
caudal fin of the ordinary osseous fishes thus : 
“The framework of the caudal fin is composed of the 
same intercalary and dermal spines superadded to the proper 
neural and hemal spines of those caudal vertebree which 
have coalesced and been shortened by absorption, in the 
progress of embryonic development, to form the base of the 
terminal fin.” (p. 67.) 
It would be very desirable to know in what fish Professor 
Owen observed this singular process of coalescence and 
absorption. So definite a statement must rest on some- 
thing more than mere supposition, .and yet it is entirely 
unsupported by any hitherto published observations with 
which I am acquainted, and is, as will be seen below, 
directly opposed by my own. 
In the excellent ‘Lehrbuch der Vergeichenden Anatomie,’ 
