A TELEOSTEAN FISH. 953 
der vordeste der falschen Dornen mit dem Dorn des letzten 
oberen Bogen verschmilzt oder es ist ein ganzer iiberziihliger 
Bogen vorhanden, so dass dann der viertletzte Wirbelkorper 
zwei obere Bogen erhiilt.” The “ Wirbelkérper” appear towards 
the end of the fourth month, doing so first in front. 
O. Hertwig (‘ Entwickelungslehre der Wirbeltiere, III. 1. 
pp. 456-82), in the account of the development of the vertebral 
column of Teleosts by Schauinsland, says :—‘ Finally, it must be 
pointed out, too, that there are vertebre in the tails of many 
Teleosts, with fully formed and equally developed double upper 
(or also both upper and lower) arches, the cartilaginous rudiment 
of which can sometimes even be shown.” It is not very clear 
what he means by the last statement. Does he mean that there 
isasingle “ Anlage” or that there are two? He continues: 
“These vertebre can be regarded: either as corresponding to 
only two sklerotome halves, in which case, however, the arches 
belonging to each half have become exceptionally developed to 
an equal extent, or (which is more probable) as having arisen by 
the later union of the two complete vertebre ; that is to say, 
at least three, perhaps even four, sklerotome halves participate, 
In these cases, then, there would be real (secondary) ‘* Diplo- 
spondyly.”” He does not bring forward any embryological evi- 
dence to prove his case, except the above-mentioned statement 
of doubtful meaning. He refers to a figure (270) of the 
“Dorsch ” (Gedus morrhua) as showing double upper and lower 
arches on the penultimate centrum, but I believe there is some- 
thing peculiar about the caudal fin-skeleton of Gadus which has 
not been described, with reference to these double-arch bearing 
centra. I understand that the appearance is due to partial 
fusion of arches and radials. 
T myself have met with the phenomenon of a centrum bearing 
double arches in the case of Trematomus newnesri, where there 
are two very well-defined neural arches on the penultimate 
centrum (see Pl. IT. fig. 13); also in the case of 7. borchgrevinki 
(see fig. 14), where, curiously, it is the antepenultimate centrum 
which bears double upper arches and double hemal arches as 
well. The penultimate centrum has greatly expanded arches, 
and, indeed, there is some slight indication of a division in the 
neural one, but the specimen was a dried skeleton and one not 
entirely free from flesh, so that I had some difficulty in making 
an accurate observation. In Votothenia macrocephala the arches 
of both antepenultimate and penultimate centra are somewhat 
more expanded than the rest, but only the penultimate neural 
arch shows any sign of division. J examined a number of allied 
forms, but did not come across any more cases of centra 
with double arches. I may mention that my drawings of the 
skeletons of the adult Pleuragramma antarcticum and Trema- 
tomus newnesit were made from specimens dissected very carefully 
in spirit, and from which every particle of flesh had been removed, 
and as much connective tissue as possible also. 
