GAS GLANDS OF SOME TELEOSTEAX FISHES. 223 



gland, of pumping in tlie nitrogen alone required. The reason for 

 the special development of the oxygen gland in many deep-water 

 fishes* is because oxygen alo»ie among the gases present in the 

 bladder is capable (in virtue of its property of combining in large 

 quantity with the haemoglobin of the blood) of being either rapidly 

 produced (by the gas gland) or vapidly absorbed (l)y the " oval ' t), 

 and this rapidity of production and absorption is essential in the 

 case of fishes which undergo consi<lerable changes of pressui-e in 

 the bladder. Deep-Avater marine or freshwater fish differ from 

 most freshwater fish in that living in gi-eat depths of water those 

 possessing migratory habits in a vertical direction require ap- 

 paratus for adapting the volume of gas in the bladder to the violent 

 changes of pressure expeiienced ; most freshwater fish, on the 

 other hand, live in comparatively shallow water — in inland lakes 

 and rivers — and thus lead placid lives, experiencing little or no 

 changes of pressure in the bladder, and for these fish it is evident 

 that thei-e is no need for the special development of an oxygen 

 gland, which makes extrava.gant use of the gas which the fish 

 requires for respiration : nitrogen and carbon dioxide sufiice t- 

 "With reference to the spherical spaces pi'esent in the cells of the 

 gas gland, Jaeger altogether denies that they represent gas 

 bubbles : they are merely vacuoles such as are to be found in 

 liver-cells, e. g. and have no connection with the production of 

 gas. Jaeger himself, however, describes gas bubbles as being 

 present in the ducts of the gas gland. Jaeger also refuses to 

 admit that the large amount of granular matter found outside 

 active glands in the bladder lumen is the product of the gas gland 

 cells : in short, represents the broken-down w^alls of exploded gas 

 bubbles. I shall discuss these features of Jaeger's theory later. 



Nusbaum & Reis (64, 55, 62-66), relying upon their extensive 

 investigations of the cytology of the gas gland, formulate certain 

 peculiar views § as to the exact mode of function of the gas gland. 

 Jaeger, as already stated, holds with Hiifner that the gas gland 

 is essentially a pumping apparatus, though he confesses entire 

 ignorance as to exactly how the individual gas-producing cell 



* Only tbose deep-water fislies wliicli migrate vertically' and thns experience 

 diflf'ereuees of pressure ; fish which remain at one depth, however great, obviously 

 have no more need for " red bodies " than have surface fish (see p. 228). 



f Any sort of gas can, of course, be eliminated by tlie pneumatic duct. 



J Mile. C. M. L. Popta in her recent paper entitled " Etude sur la Vessie A^rienne 

 dcsPoissons" (Ann. Sci. Nat. Zool.,t. xii, 1910, pp. 1-160) comes to the conclusion 

 that " la vessie aerienne des poissons se developpe pour aider a la circulation de 

 I'oxygene [et en general des gaz] dans le corps du poisson." I confess that this 

 conclusion does not convey much meaning to me. I entirely fail to understand why 

 the fish should develop an organ for the sole purpose of liberating oxygen into the 

 blood in the same way I suppose that tlie liver liberates food material, and this is the 

 only intelligible proposition which the author's conclusion conveys to me. Though 

 the bladder undoubtedly in many cases performs this function incidentally, yet tlie 

 fact that the bladder often contains other gases (nitrogen and carbon dioxide) the 

 presence of which in the blood cannot be of the slightest advantage to the animal, 

 shows that this storage function of the bladder cannot be its primarj' function. I 

 cannot see that the author's conclusion in any way explains the diflcrdnt proportions 

 in vrhich the three principal gases occur in the bladder. 



§ Unfortunately adopted in the last edition of Wiedersheim's ' Vergleichende 

 Aiiatomie der "Wivbelthiere,' Siebentc Aufiage, 1909. - 



