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modes of connection with the internal ear, mostly by tubular 
prolongations of the air-bladder, or a connecting chain of 
auditory ossicles. 
Among the Physoclisti, the majority of which are marine, we 
find the air-bladder as a closed sac, having a single cavity, as 
observed in many of the Percide, wherein its greatest length is 
in its longitudinal axis. In some forms, as Holocentrwm and 
Sargus, cecal processes of the air-bladder diverge to attach 
themselves to the membrane, closing the part of the otocrane 
containing the sac of the great otolite:’ (Owen). It has 
likewise been remarked that in the scad or horse-mackerel, 
Caran trachurus, a canal passes from the air-bladder to the 
bronchial cavity, permitting the escape of air, although it does 
not serve to admit it.—(A. Morzav, Compt. Rend. Ixxx. pp. 
. 1247—1250.) Kwer observed that in several fishes provided 
with pectoral pores, the thymus gland is absent, and the air- 
bladder communicates with the cesophagus by an open duct, 
in some Acanthopterygians, as Holocentrum, Priacanthus, Cesio, 
&c.—(Sitz. Ak. Wiss. Wien. 1864, xlix, May, pp. 455—459). 
The air-bladder may have lateral attachments, as in Sciena, or 
blind appendages, as in Polynemus. The interior of the air- 
bladder of physoclisti, as the cod, is lined with a thin membrane 
of silvery whiteness, composed of a series of fibres, covered 
with a basement membrane, provided with scales of epithelium ; 
beneath this is a layer of vessels, while inside is situated a 
highly vascular body, receiving blood direct from the aorta: 
capillaries exist, and here veins commence. In the perch the 
glandular body is not in one compact mass, but scattered about 
its interior —(Quexert, Trans. Microp. Soc., i, 1844, p. 100). 
If we examine the Physostomi, or those families in which a 
pneumatic duct exists throughout life, forming a communication 
between the interior of the air-bladder and the upper portion 
of the alimentary canal, we find the majority of such are fresh- 
water forms,* situated between the Physoclisti on one hand 
* The majority of marine Physostomi are littoral, or surface swimmers, 
often weak forms, which have to escape pursuit of enemies while rapidly 
rising to the surface. 
