272 LECTURE XI. 



peritoneum to the hinder end or bend of the stomach, or to the 

 beginning of the intestine : it is of variable but commonly triangular 

 shape ; of a deep red or brown-red colour, and soft and spongy : the 

 venous cells of which it is chiefly composed are filled with granular 

 corpuscles. 



LECTURE XL 



PNEUMATIC AND RENAL ORGANS. 

 AIR-BLADDER. 



The organ so denominated is found, in most osseous fishes, in the 

 form of an elongated bladder, tensely filled by air, extending along 

 the back of the abdomen, between the kidneys and the chylopoietic 

 viscera, and sometimes (G?/?nnotus, Ophiocephalus, Coins) beneath 

 the caudal vertebrte to near the end of the tail. It is seldom bifur- 

 cated (as we see it in some species of Diodon, Tetrodon, Dacty- 

 lopterus, Pimelodus, Prionotus) ; still more seldom divided length- 

 wise into two bladders {Arins, Gagora, Polypterus, Lepidosiren, 

 Jig.7\.p,p) : it is oftener divided crosswise into two compartments, 

 which intercommunicate by a contracted orifice {^Cyprinidce, Jig. 58. 

 p q, Characinidce) ; or are quite separate {Bagrus JUamentosus, 

 Gymnotus equilabiatus.) In the Siluroid genus Pangasius the air- 

 bladder is divided into four longitudinally succeeding portions. In 

 the Trigla hirundo the swim-bladder is notched anteriorly by one 

 indent, and posteriorly by two indents, from which notches septa 

 project inwards : sometimes the air-bladder is divided partially, both 

 lengthwise and crosswise (^Cobitis fossilis, Auchenipterus furcatus, 

 some species of Pimelodus). Sometimes the bladder sends forwards 

 two blind processes from its forepart {SphyrcEna barracuda, Trigla 

 cuculiis, Conodon antillanus, some species of Micropogon and Oto- 

 lithus) ; sometimes from its hind part {^Cantharis vidgaris, Lethrinus 

 atlanticus, Heliases insolatus, some species of Sillago, Mcuna, and 

 Smarts) ; sometimes from both ends {Dules maculatus, Pimelipterus 

 altipennis, Lactarius delicatulus). The Bearded Umbrina has three 

 slender csecal processes from each side of its air-bladder ; the allied 



