274 OBSERVATIONS ON THE DEVELOPMENT OF 
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 something more than mere suppo- 
sition, 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, by 
Von Siebold and Stannius (1846), the latter (‘ Wirbelthiere,’ p. 10) 
considers the vertical caudal plate to be produced by the coalescence 
of the superior and inferior arches, interhamal and interneural bones 
“of the posterior caudal vertebra or of many of the caudal vertebre ;” 
and in a note it is added, that the commencement of the process may 
be clearly traced in the pike. 
A valuable paper published by the late eminent ichthyologist, 
Heckel, in the ‘Sitzungs-berichte der Kaiserlichen Akademie der 
Wissenschaften’ for 1850 (p. 143 et seq.), contained the first accurate 
and comprehensive account of the structure of the piscine tail, and 
threw quite a new light on the general doctrine of the relation between 
ancient and modern fishes. 
“The few now-living successors of the bony Ganoids with com- 
plete vertebree, which first appeared in the Jurassic period—our 
Lepidosteus, Polypterus, and probably also Aimria (the latter of which 
I have had no opportunity of examining)—still have quite imperfect 
terminal vertebra, behind which a part of the chorda persists in 
a perfectly unossified state. At the same time these terminal 
vertebrae appear to be developed in quite a different way from those 
of ordinary Teleosteans, for the arrested commencements of the 
posterior caudal vertebre, or their first centres of ossification, appear, 
not as in the latter, above and below at the base of already formed 
‘spinous processes, but at the sides of the chorda, before either spinous 
processes or vertebral arches are developed. They become thick- 
ened anteriorly, and penetrate like wedges towards the axis of the 
chorda. Indeed, it would seem, from the fact that different indi- 
viduals of these fishes, without distinction of size, present a consider- 
able variation in the number of their terminal vertebrae (which may 
be even perfectly developed) as if they constantly added new 
vertebree, whereby the end of the vertebral column—that is to say, 
the still naked chorda—must gradually, if not perfectly, be converted 
into ossified bodies of vertebra. ..... 
“ Another group of fishes, or rather of the now-living Zeleosted 
