GLANOMORPHS. 
these growths, but are furnished instead on each side of 
the body with a long, cylindrical duct penetrating into 
the dorsal muscles, a backward continuation of the 
branchial cavity, containing a respiratory sac which is 
lined with a continuation of the mucous membrane 
of the said cavity. This continuation of the mem- 
brane is abundantly furnished with ramifications of the 
branchial arteries (the first artery on the right side, the 
last on the left"), which convey hither a great portion 
of the venous blood of the heart. The blood oxyge- 
nated in each of the respiratory sacs by inhaled air * 6 is 
partly carried off by arterial ramifications in the sur- 
rounding muscles, but most of it is collected in a main 
artery, that discharges it into the great dorsal artery. 
The whole of this arrangement, it is true, stands in a 
physiological respect beside the structure just described 
in Heterobranchus and Clarias; but the form of the body 
and the structure of the fins range Saccobranchus im- 
mediately beside Silurus. An amphibious manner of 
life has produced a development of special respiratory 
organs for the breathing of air; but nevertheless the 
natural kinship may be most safely expressed by the 
form of the body and the structure of those external 
organs which otherwise afford the most tenable cha- 
racters within this series of families. 
This is also true of the variations of the air-bladder. 
In our Sheatfish it is externally simple, but internally 
divided in a longitudinal direction. In Bagrus these 
divisions are transverse. In Malapterurus c the anterior 
part is externally set off, though not internally divided, 
from the posterior, which is partitioned internally, though 
incompletely, both in a longitudinal and a transverse 
direction; and the anterior part itself is externally di- 
vided in a longitudinal direction into two oval chambers, 
which communicate, however, with each other internally. 
In BMnolepls d the posterior part of the air-bladder has 
disappeared, and the two oval, anterior chambers lie 
side by side, each enclosed in an osseous capsule. These 
among other variations in the structure of the air- 
bladder in the different Glanomorphous genera show 
that the form of this organ is highly plastic; but up 
“ Hyrtl, Stzber. Akad. Wiss. Wien, Math. Naturw. CL, Bd. 1 
6 This according to Day. Gunther states, however, ( Introd . 
vity receive water. 
c Geoffroy, Descr. cle VEgypte , Poiss ., pi. XII, fig. 4. 
d Reissner, Arch. Anat., Physiol., 1859, p. 421, Plate XII. 
e Stzber. Akad. Wiss. Wien, Math. Nat. Cl., Bd. XI, p. 145. 
f Fishes of India , p. 440. 
a Weber, De aure et auditu etc., Lips. 1820, p. 53. 
h Sorensen, Om Lydorganer hos Fislce, Kbhvn 1884, p. 121 
691 
to the present the differences are far too little known 
to be employed in the system. Kner also came to 
the conclusion 6 that within the Boras group the diffe- 
rences in the form of the air-bladder may well be em- 
ployed in the distinction of the species, but not in the 
definition of the genera. Day 7 has, however, employed 
these relations in the classification of the genera; but 
he remarks on this head that the marine Glanomorphs 
in general have a thick air-bladder, not enclosed in an 
osseous capsule, as well as the majority of the fresh- 
water forms; but that the further we penetrate into the 
highlands of India, the oftener we meet with Glano- 
morphs whose air-bladder is cased in this manner. It 
would thus seem that here too the amphibious manner 
of life exerts a determinative influence. 
The incasement of the air-bladder is also merelv a 
J 
part of the marked ossification that takes place in the 
anterior portion of the spinal column. Here, as we have 
mentioned, the anterior vertebrae are more or less com- 
pletely confluent; and their ribs are transformed into so- 
called acoustic bones (Weberian ossicles 7 ), which serve to 
connect the air-bladder with the organs of hearing, and 
may well deserve their name, though they do not pos- 
sess the least homology with the otosteals ( ossicula 
auditus ) of the higher Vertebrates. Here this ossifica- 
tion of the first vertebrae — conjoined in many Glano- 
morphs with occipital plates (interneural growths) — 
forms a strong support for the spinous ray of the first 
dorsal fin, one of the powerful weapons of these fishes. 
Both these structures are also connected, according to 
Sorensen, with the power possessed by several Glano- 
morphs of producing sounds 6 . The dorsal spines — the 
rudimentary (first) and the great (second) spinous ray — 
produce noises (like the spinous ray of the pectoral fins) 
by means of the friction between their articular surfaces 
and those of the interspinal bones; and the air-bladder 
utters sounds partly in the same way as in the Gur- 
nards, Filefishes, and others (see Part I), partly by 
means of the vibration produced by the violent contrac- 
tion of the special muscles running from the occipital 
region or the foremost (confluent) vertebrae to the acous- 
.1 (1853), p. 305. 
'itudy Fish., p. 565) that the lung-like extensions of the branchial ca- 
ete. 
