^ 



22S DU. \V. N. F. WOODLAXD OX THE 



sebaceous gland is not called upon for this degree of self-sacrifice. 

 Finally, the researches of Deineka (29) on the intimate nerve- 

 supply of the cells of the gas gland — ^it being stated that each 

 gland cell is surrounded by a terminal cluster of nerve-filaments — 

 and the known nervous control of the gas gland by two kinds of 

 fibres running in the vagus and sympathetic nerves respectively 

 (Moreau, 50, 51, 53 ; Bohr, 20 ; and others) render it very im- 

 probable that such cells undergo the wasteful decomposition 

 assumed by Nusbaum & Reis. 



I have now discussed the main features of the rival theories 

 of Jaeger and Nusbaum & Reis. If we eliminate the errors 

 and combine the truths of both with some observations of 

 other authorities, we arrive at the following outline statement 

 of the mode of working of the gas gland. The gas gland, in some 

 unexplained manner, but probably, as Jaeger suggests, by the 

 secretion of a toxin (which Reis. & JSTusbaum suggest he should 

 have figured !) so influences the blood conveyed to it as to cause 

 the disintegration of a certain proportion of red blood corpuscles. 

 This fact of the disintegration is admitted by Bykowski and 

 Nusbaum & Reis. The disintegration of the erythrocytes 

 is primarily for the purpose of enabling the gas gland 

 cells to "lay hold " of the relatively large quantity of oxj^gen 

 contained in the blood. Oxygen, in consequence of its easy 

 obtainment from the blood, is the all-important gas required by 

 iishes which undei-go consideiuble and rapid changes of pressure 

 in their bladder consequent on rapid changes in their vertical 

 position, and the gas gland, considered as a special development 

 of the lining epithelium of the bladder, is solely concerned with 

 the rapid production of oxygen. The gas gland being essentially 

 an oxygen gland is therefore most developed in those fishes which 

 possess the greatest proportion of oxygen in their bladder gas ; in 

 iishes like the Oyprinidie and some other freshwater families, on 

 the other hand — iishes which exist in inland waters possessing 

 little depth and which cannot, thei^efore, experience great changes 

 of pressure in their bladder by vertical displacement, — nitrogen 

 and carbon dioxide form the principal constituents of the bladder 

 gas * and gas glands, in the ordinaiy sense of the word, and retia 

 mirabilia are absent. It was formerly supposed that a large 

 proportion of oxygen in the bladder was associated with the great 

 depth at Avhich the fish existed — the greater the depth the greater 

 the percentage of oxygen, — but apparently this is not altogether 

 the case f. A large proportion of oxygen, as already stated, seems 

 to be, for the most part, associated with the habits of those fish 

 which frequently make considerable excursions in a vertical 

 direction : if the fish sinks, the oxygen gland becomes active and 



* Cvprinus cai'pio contains about 94 per cent, of nitrogen in its bladder (Hiifner). 



t C'f. JSxocoetus volitans, tlie Flj'ing-tish, an essentially surface marine form, 

 possessing, according to Humboldt (41), 94 per cent, of nitrogen in its bladder, with 

 Coreqonus acronius, a fresliwater form living permanently at a depth of over 

 seventy metres and possessing, according to Hiifnei", about the same percentage of 

 nitrogen, and many other examples might be quoted. 



