AIR-BLADDER OF FISHES. 



495 



328 



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

 of the capillaries 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 having 

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

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

 vein, which empties itself into the mesenteric, perforate together 

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

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

 and subdivide upon the mucous membrane : the arterioles 

 frequently 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,' which 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 corpuscles, which de- 

 pend in two rows from each 

 vascular branch, and are bound 

 together by a loose cellular 

 tissue : the corpuscles are beset 



With fine villiform processes. Superficial and looped vessels of the vaso-ganglion 

 mi ITT f .1 air-bladder, Cod. CCLXVIII. 



Ihe 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 

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

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

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



" O O c5 



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

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

 again branch to form the common capillary system of the lining 

 membrane of the air-bladder. 



Eathke l failed to detect the opening of the air-duct with the 

 1 cxi. 'Ueber die Schwimm-blase einiger Fische,' p. 98. 



