144 THE WAYS OF BREATHING 



are continued without interruption from the one 

 to the other system, shows how the transition 

 could be effected, but it does not, in my opinion, 

 necessarily support Spengel's and Goette's theory 

 of the origin of vertebrate lungs and air-bladders 

 from gill-pouches. 1 This is an interesting theory, 

 and adds weight to the conception of the gill- 

 cleft as an autonomous "morphon," but there are 

 difficulties in the way of its acceptance. In the 

 first place, from the analogy of hydrostatic organs 

 in other phyla, it does not seem necessary to 

 invent a factitious explanation of the air-bladder 

 as a gill-pouch derivative ; the accumulation of 

 air or gas in air-chambers is a widely distributed 

 phenomenon, and in some fishes {e.g., the Globe 

 Fishes) the oesophagus itself can be converted 

 into an air-chamber at the will of the animal. 



There seems to be no particular difficulty in 

 supposing that the air-bladder arose as a single 

 or paired diverticulum of the fore-gut for the 

 storage of air ; and whether the first function 

 was respiratory or hydrostatic or both, is another 

 question. 2 Spengel lays great stress upon the 



1 J. W. Spengel, " Ueber Schwimmblasen, Lungen und Kiemen- 

 taschen der Wirbelthiere," Zool. Jahrb. Sufipt, 1904, pp. 727-749. 

 In this paper the term "morphon" is suggested; it means a 

 morphological unit or element. 



1 Facts in support of the view that the original function of the 

 air-bladder was respiratory were brought forward in a paper by 

 Charles Morris on " The Origin of Lungs, a Chapter in Evolution," 

 in The American Naturalist, vol. xxvi., 1892, pp. 975-986. This 

 opinion is tentatively supported in principle by Hubrecht (loc. a'/., 

 1908), who refers to Assheton's paper on " Gymnarchus" in the 

 Budgett Memorial Volume. 



