. The Cambridge natural history. Zoology. 302 FISHES (a) The air-bladder is by no raeans universally present in Teleosts. It is absent in several entire families/ such as, 'for example, the Flat Fishes or Pleuronectidae, the Scopelidae, and the " Lump-suckers " (Cyclopteridae). In a few families, as in the Mackerels (Scombridae), the " Blennies " (Blenniidae) and the Polynemidae, the organ is present in most genera, but absent in a few, or even present or absent in different species of the same genus. Thus, of the three British species of Mackerel, viz. the Spanish M
. The Cambridge natural history. Zoology. 302 FISHES (a) The air-bladder is by no raeans universally present in Teleosts. It is absent in several entire families/ such as, 'for example, the Flat Fishes or Pleuronectidae, the Scopelidae, and the " Lump-suckers " (Cyclopteridae). In a few families, as in the Mackerels (Scombridae), the " Blennies " (Blenniidae) and the Polynemidae, the organ is present in most genera, but absent in a few, or even present or absent in different species of the same genus. Thus, of the three British species of Mackerel, viz. the Spanish Mackerel (Scomber colias), S. pneumatophortts, and the common Mackerel (S. scombrus), an air-bladder is present in the first two, but absent in the third.^ (5) As might be anticipated, the shape of the air-bladder is extremely different in various Teleosts, and usually conforms to the shape of the body, while Fig. the structure of one differences in relative size are ot the larger alveoli of the air-bladaer of Protopterus. 1, Central cavity of of frequent Occurrence, even in the lung; 2, alveolus; 3, tubular ^j^ggj related spccics. Some- cavities communicatmg with 4, the ^ •> '^ small terminal sacculi. (From Bald- times the organ is more or leSS win Speucer.) tubular, fusiform, ovoid, or heart- shaped ; occasionally it is shaped like a " dumb-bell,'' consisting of two lateral sacs connected by a median tubular portion, as in the Siluroids Glarias and Gallichthys; or it may be horse-shoe-shaped, as in the Silurid Ailia^ Not unfrequently a transverse constriction divides the air-bladder into two inter- communicating sacs, as in most of the Carp family (Cyprinidae), or three such sacs may be formed by two constrictions ( Opliidiuvi). In the " Electric Eels " (G-ymnotidae) there are two sacs, connected by a slender canal, from which the ductus pneumaticus takes its origin.* The air-bladder is either more or less free in the abdominal cavity, or f
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
