308 FISHES CHAP, 
morrhua), 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 
A B 
Fic. 184.—Red glands, A, of the Cod (Gadus morrhua), and B, of the John Dory (Zeus 
Jaber), seen from the interior of the air-bladder. 6v, Blood-vessels ; 7.g, red glands. 
(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 hfe there are 
either no special retia mirabilia, or, as in the Kel, only the 
so-called “red bodies,” ? 
1 For the blood-supply of the air-bladder see Chap. XII. 
