gas glands of some telbostean fishes. 193 



Ophichthys (Ophisurus) serpens L. 



The general plan of the tioo retia mirabilia and the gas gland 

 is exactly that found in Angailla. The epithelial lining is, as 

 ill Angailla, squamous and covers projections of the subjacent 

 connective tissue, which contain, not one large capillary, but many 

 small ones. Posteriorly the lumen of the duct, which anteriorly 

 is circular in transverse section, becomes very I'estricted and star- 

 shaped in outline, owing to the great size of the connective tissue 

 projections just mentioned — a feature not met with in the species 

 described above. The epithelium of the bladder wall is hardly 

 folded at all over the greater part of its area, simply consisting 

 of a single layer of short columnar glandular cells, but in places 

 folding occurs, occasionally to such an extent as to resemble 

 the bladder epithelium of Angicilla, but this is rare. 



It is curious how the epithelial linings of the duct and bladder 

 differ in these four closely related fish — Aiiguilla, Myrus, Ophichthys 

 imberbis, and 0. serpens. In the duct and bladder of Anguilla Ave 

 have the extremes of flattened and folded epithelia ; in the other 

 genera intermediate conditions of the epithelium exist, both ns 

 regards the form of the cells and their arrangement, and the duct 

 and bladder epithelia are not sharply distinguishable from each 

 other, and yet the vascular supply has the same distribution in all 

 cases, although it undoubtedly varies considerably in amount, 

 being much greater in the Eel than in the other genera. The 

 diflTerent conditions of the rete mirabile in the two species of 

 Ophicthys are also noticeable. 



The ty^Q of vasculo glandular apparatus found in the bladders 

 of the preceding genera may be defined as follows : the glandular 

 epithelium is composed of a single layer of cells which either 

 remains unfolded or is only simply folded, and the retia mirabilia 

 a,re one or two in number and are large and distinctly sepai-ate 

 from the gas gland, the capillaries of the rete reuniting to form 

 large arteries and veins before coming into connection with the 

 glandular epithelium. 



A Second Type of Bladder Vasculo-glandidar Apparatus, 

 as exemplified in Syngnathus acus Mich. 



Syngnathus acus is a physoclistous fish in possession of a " red 

 body," which is, on the whole, very similar in construction to that 

 of the Eel, but which nevertheless exhibits certain differences 

 which justify us in separating it as a distinct type. The "red 

 body " in Syngnathus is visible with tbe naked eye as a small 

 red patch at the extreme anterior end of the bladder. An artery 

 and vein running in the anterior attachment of the bladder divide 

 up in the manner already described for the Eel to form the single 

 rete mirabile (Pis. II. & III. figs. 1 0-14). It will also be observed in 

 figures 10 and 11 that posterior extensions of the diffuse pancreas 

 (indicated in the figures by yellow masses) penetrate into the 

 anterior end of the I'ete mirabile and, as will be shown in detail 



