3o8 



FISHES 



CHAP, 



morrhna), the Haddock {G. aeglefinus), and the Hake (Merluccius 

 vulgaris), 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 



18^-— Red glands, A, of the Cod {Oadus morrhua), and B, of the John Dory (Zms 

 faber), seen from the interior of the air-bladder, bv. Blood-vessels ; r.q, red "lands 

 (From Swale Vincent and Stanley Barnes.) ' »• o 



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 

 £o-called " red bodies." ^ 



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



