GAS GLANDS OF SOME TELKOSTEAN FISHES. "219 



of the theory advanced in Part II., is the distribution of the 

 granular matter in the capillaries of the rete mirabile. Careful 

 examination of my sections* of Gohius niger, Gobius minutus, 

 Syngnathus acus, Peristethus caiaphr actus, Gasierosteus splnachia, 

 and some others, in all of which the gas glands are more or less 

 active, had led me to the conclusions that granular matter is 

 present in the venous capillaries of the rete to a far greater extent 

 than in the arterial, and that the relatively small amount of 

 granular matter present in the arterial capilLiries is chiefly 

 situated next the distal pole of the rete — the pole next the gas 

 gland. The small calibre of the arteries compared with the veins 

 and the few series of sections of active glands, well fixed and well 

 stained, wdiich I possess render it difficult to be absolutely certain 

 of the above conclusions, but I am as certain as the limitations of 

 my material will permit me to be. The bearing of these facts on 

 the theory already outlined on page 198 is perhaps already 

 apparent, but I shall reserve discussion for Part II. (see p. 232). 



As already implied, teleost gas glands aj-e best classified 

 according to the character of the glandular epithelium. We 

 divide gas glands into two groups: — (1) gas glands in which the 

 glandular epithelium is a single layer, which may either remain 

 unfolded or become folded in variable degrees ; and (2) gas glands 

 in which the glandular epithelium is many-layered, the mass of 

 cells being penetrated by fine ducts. With the exception of a few 

 cases [Trigla gurnardus, Smarts maurii, S. vulgaris, and some 

 others) in which the much-folded epithelium has secondarily 

 assumed a massive character, this massive type of epithelium is 

 probably not derivable from the folded type. Also in this second 

 group of gas glands the rete mirabile is always contiguous with 

 the glandular epithelium, reunion of the cajjillaries never 

 occurring [Ophidium, Fierasfer, Box, Atherina, Coris, Balisies, 

 Sargus, Caraiix, Charax, Herranus, Zeus, Gadus, Cepola, Esox, 

 Perca, &c.). 



Group 1 is subdivisible into two minor groups : — 



(a) The rete mirabile of the gas gland consists of either one 

 or two bodies distinctly separate from the glandular 

 epithelium, the capillaries of the rete reuniting to form 

 large arteries and veins before they come into con- 

 nection with the glandular epithelium {Angtdlla, 

 Myrus, Ophichthys, Muraena, &c.). 



(h) The rete mirabile of the gas gland is contiguous with the 

 glandular epithelium, although a small amount of re- 

 union of the capillaries occasionally occurs {Syngnathus, 

 Gohius, Siphonostoma, Kerophis, Gasierosteus, Peri- 

 stethus, Trigla, &c.). 



In concluding this account of the practical work connected with 



* Observations of tbe rete mirabile, when sectioned loiigitndinallj', are preferable 

 from tins standpoint ; tbe arterioles are. of course, distinguishable from the venules 

 bj thicker walls, by small calibre, and by the peculiar endothelium before mentioned 



