AIR-BLADDER OF FISHES. 



495 



radiating tufts (Pilcc) ; in both without any special aggregation 

 of tlie capilhiries to form a ' vaso-ganglion.' 3. The conversion 

 of the tufts by rapid subdivision into capillaries aggregated so as 

 to form red gland-like bodies ; the capillaries reuniting into larger 

 vessels, which again ramify richly round the border of the gland- 

 like body ; the rest of the inner surface of the air-bladder liaving 

 tiie ordinary simple capillary system (Perch and Cod). In the 

 Cod-fish, a large artery, a branch of the cocliac, and a still larger 

 vein, winch empties itself into the mesenteric, perforate together 

 tlic fibrous tunic of the swim-bladder. Before they reach the 

 inner surface, they divide into some branches, which then radiate 

 and srdjdivide upon the mucous membrane : the arterioles 

 freijuently anastomose together, and the venules as frequently 

 anastomose with each other: both are inextricably interwoven, 

 and form the basis of the so-called 'air-gland,' whicli is essentially 

 a large ' bipolar rete mirabile,' or vaso-ganglion. The ultimate 

 vessels of this body form loops, 

 where the arteries return into 

 veins, fig. 328, and these loops 

 are covered by a layer of vessels 

 and epithelium, a, a. This organ, 

 however, is further composed of 

 a number of peculiarly arranged, 

 elongated cor2)uscles, which de- 

 pend in two rows from each 

 vascular branch, and are bound 

 together l^y a loose cellulai 

 tissue : the corjmscles are beset 

 with fine villiform processes. 

 The blood returns from the vaso- 

 ganglions by small veins which rarely accompany, more commonly 

 cross, the arteries. 4. The two chief ' retia mirabilia,' or vaso- 

 ganglions, in the air-bladder of the Eel and Conger, which are 

 situated at the sides of the opening of the air-duct, are also 

 'bipolar,' and consist of both arterioles and venules: they consist 

 of straight parallel cajiillaries, as in fig. 329 : their efferent trunks 

 do not ramify in the immediate margin of the vaso-ganglion from 

 which they issue, as in the vaso-ganglions of the Cod, Burbot, 

 Acerlne, and Perch, but run for some distance before they 

 again branch to form the common capillary system of the lining 

 membrane of the air-lsladder. 



Kathkc ' failed to detect the opening of the air-duct with the 

 ' CXI. ' Ucber die Schwimm-Uase cinigcr Fischc,' p. 98. 



Superllcial nnd lonpcd vessels uf the \asu-g;ni'-,']ien 

 air-liladtler, Cua. cci.xvni. 



