190 DR.. W. N. F. WOODLAND ON THE 



(that is, M*laen the duct opens into the bladder) it then assumes 

 the glandular folded character of the bladder epithelium, were it 

 not for the fact that in other physostomous genera this sharp 

 distinction between duct- and bladder-epithelium is absent, as I 

 sha,ll show shortly. 



The intracellular structures described in detail below as being 

 present in the cells of the gas glands of other teleost fishes — 

 intracellular gas bubbles, capillaries, and ducts — are not easily to 

 be detected in my preparations of the Eel, but I believe I have 

 seen ga,s bubbles present in a few cases, also the capillaries 

 occasionally intrude somewhat upon the cells at their bases. 

 Granular matter, ejected into the bladder- cavity with the gas, is 

 so small in aanount in the gland ducts of my preparations that it 

 may be said to be absent. 



The folded glandular epithelium of the gas gland of the Eel, 

 and presumably of all other genera possessing a folded epithelium, 

 originates from a single unfolded layer which during development 

 becomes pushed out into the folds by the activity of the large 

 ca.pillaries situated in the thin layer of connective tissue- lying 

 at the base of the epithelium *. 



Thus in the type of " red body " found in the Common Eel 

 we have two large retia rairabilia,, situated some distance from 

 the epithelium of the bladder which they supply, and the greater 

 part of this lining epithelium of the bladder is glandular and 

 folded in a simple manner to form the gas gland. In all " red 

 bodies " we have these two elements, the rete mirabile and the gas 

 gland, but in the majority of " red bodies " these two elements 

 are much more intimately associated with each other and more 

 complex in form as compared with the structure of the simple type 

 of " red body " just described. The Eel type of " red body " serves 

 as a convenient starting-point for considering more complex types. 



Before considering these types, it is necessary to point out a 

 serious mistake contained in almost the only English paper 

 dealing with the present subject, that of Vincent and Barnes (75), 

 which, though the paper is now quite out of date, has found its 

 way into at least one recent text-book (' Cambridge Natural 

 History,' vol. vii. 1904, p. 308). Vincent and Barnes, following 

 Coggi (25), state that " red glands are only found in those 

 bladders which are devoid of a ductus pneumaticus," and they 

 draw a sharp distinction between Physoclisti, which possess the 

 gas gland, and Physostomi, which are supposed to be devoid of 

 one. I need hardly say that no such distinction exists. Vincent 

 and Barnes are right, in so far as they say that the " red bodies " 

 of the Eel are only partially comparable with those of the 

 Gadidse {vide supra), but it is difficult to understand how they 

 came to overlook the large and conspicuous glandular epithelium 

 lining the bladder cavity. Further, as Deineka (29) points out, in 

 the physostomous Pike {^Esox hocitos) a conspicuous gas gland 



* I am much indebted to Dr. W. G. Ridewood for kindly presenting mc with 

 most of my young material. 



