_Collichthys_[344] has a still more remarkable arrangement. In this Sciaenoid (Fig. 183) twenty-five tubular branches are given off from each side of the bladder, all of which soon subdivide into a dorsal and a ventral division. These still further divide, and their branches either end blindly or are prolonged into a series of arches to the mid-dorsal or mid-ventral line as the case may be, where they become continuous with the corresponding branches of the opposite side. The series of dorsal branches, enveloped in their peritoneal investment, extend between the body of the air-bladder and the roof of the body-cavity, while the corresponding ventral branches, similarly invested, surround that part of the coelom which contains the stomach, intestine, and liver. [Illustration: FIG. 181.—Air-bladder of _Corvina lobata_. (From Cuvier and Valenciennes.)] (_d_) In addition to the subdivision of the cavity of the air-bladder by the externally obvious, {305}transverse, or longitudinal constrictions already described, or by the growth of simple or branched prolongations, the organ is often chambered or sacculated by the development of internal septa or partitions. [Illustration: FIG. 182.—Air-bladder of _Pogonias chromis_. (From Cuvier and Valenciennes.)] In many of the Gurnards (_Trigla_)[345] the cavity of the bladder is divided into two intercommunicating compartments by a transversely-disposed and centrally-perforated diaphragm. The large air-bladder of some species of _Erythrinus_[346] is subdivided internally into numerous alveoli or sacculi. In _Notopterus_ a longitudinal septum divides the cavity of the abdominal portion of the bladder into two lateral chambers, which, however, freely intercommunicate anteriorly. In the great majority of the Siluridae[347] the cavity of the organ is divided by a characteristic T-shaped arrangement of a primary transverse and a longitudinal septum into three communicating chambers, of which one is anterior and transversely disposed, and two are posterior and longitudinally arranged (Fig. 222). The posterior compartments in many genera are still further divided by the growth of secondary transverse septa, extending outwards from the median longitudinal septum, without, however, reaching the external lateral walls of the chambers. In a few genera, as in certain species of _Pangasius_,[348] additional fibrous bands and ridges passing between the primary and secondary {306}septa give to the cavities of the lateral compartments the appearance of being occupied by a coarse spongy network. [Illustration: FIG. 183.—Transverse section through the abdominal region of _Collichthys lucida_. _a.b_, Air-bladder; _d.b_ and _v.b_, the dorsal and ventral branches of the air-bladder; _l_, liver; _m_, mesentery; _s_, stomach; _v.c_, vertebral column. The dotted and broken lines surrounding the bladder and its branches represent the peritoneal investment of these parts. (From Günther.)]