308 



FISHES 



CHAP. 



morrhua), the Haddock (G. aeglefinus), and the Hake (Merluccius 

 mdgaris), have a single large " red gland " projecting into the 

 interior of the bladder from its dorsal or ventral wall (Fig. 184, A). 

 The John Dory (Zeus faber} has five such glands, worm-like and 

 curved in shape, with their concavities facing a central point 

 between them (Fig. 184, B). In these Fishes a "rete mirabile " 

 of blood-vessels forms the vascular basis of the glands. The 

 ordinary pavement epithelium of the bladder becomes replaced 



FIG. 184. Red glands, A, of the Cod (Gadus morrhua), and B, of the John Dory (Zeus 

 faber), seen from the interior of the air-bladder, bv, Blood-vessels ; r.g, red glauds. 

 (From Swale Vincent and Stanley Barnes.) 



by faintly granular, columnar, and evidently glandular cells as 

 it passes over the retia mirabilia, and at the same time becomes 

 invaginated into the mass of capillaries in the form of a number 

 of simple caecal glands (Fig. 185). So far as is at present 

 known, the " red glands " are only found in those Teleosts in 

 which the air-bladder has no ductus pneumaticus, whereas in 

 those Fishes which retain the ductus throughout life there are 

 either no special retia mirabilia, or, as in the Eel, only the 

 so-called " red bodies." x 



1 For the blood-supply of the air-bladder see Chap. XII. 



