Air-bladders without duct are found in Acanthopterygians, Pharyngognaths, Anacanths, and Lophobranchs. They may consist of a single cavity or divided by constrictions into two or three partitions situated behind one another; they may consist of two lateral partitions, assuming a horseshoe-like form, or they may be a single sac with a pair of simple or bifid processes in front or behind (Fig. 61). The families of _Sciænidæ_ and _Polynemidæ_ possess air-bladders with a most extraordinary development of appendages rising from each side of the air-bladder. In the Sciænoid (Fig. 63) fifty-two branches issue from each side, each branch being bifurcate and bearing smaller appendages. In _Pogonias chromis_ (Fig. 64) the sides of the anterior half is provided with irregular broad-fringed appendages, the hindmost of which communicates by a narrow duct with the posterior extremity of the air-bladder. In _Collichthys lucida_ (Fig. 62) twenty-five appendages issue from each side; the anterior ones are directed towards the front, but the lateral assume a more posterior direction, the nearer they are to the posterior extremity of the air-bladder, where they form an assemblage giving the appearance of a cauda equina. All these appendages soon bifurcate in a dorsal and ventral stem; these stems bifurcate again and again, and either terminate after the first or second bifurcation or are so far prolonged as to reach the median line of the ventral and dorsal sides, anastomosing with the branches of the other side. The branches being enveloped in laminæ of the peritonæum, form a dorsal and ventral sac of beautiful appearance, caused by the regular arrangement of the air-vessels. The dorsal sac is situated between the air-bladder and the roof of the abdominal cavity without being attached to the latter. The ventral sac receives within its cavity the intestine, liver, and ovaries.--A peculiar mechanism has been observed in the air-bladder of the _Ophidiidæ_, the anterior portion of which can be prolonged by the contraction of two muscles attached to its anterior extremity, with or without the addition of a small bone. [Illustration: Fig. 63.--Air-bladder of a Sciænoid. I. Visceral surface opened at _b_, to show openings of the lateral branches. II. Isolated lateral branch; _a_, its opening into the cavity of the air-bladder.]