CHAPTER XXI 

 LABYRINTHICI AND HOLCONOTI. 



! HE Labyrinthine Fishes. An offshoot of the Percomorphi 

 is the group of Labyrinthici, composed of perch-like 

 fishes which have a very peculiar structure to the 

 pharyngeal bones and respiratory apparatus. This feature is 

 thus described by Dr. Gill: 



"The upper elements of one of the pairs of gill-bearing 

 arches are peculiarly modified. The elements in question 

 (called branchihyal) of each side, instead of being straight 

 and solid, as in most fishes, are excessively developed and pro- 

 vided with several thin plates or folds, erect from the surface 

 of the bones and the roof of the skull, to which the bones are 

 attached. These plates, by their intersection, form chambers, 

 and are lined with a vascular membrane, which is supplied 

 with large blood-vessels. It was formerly supposed that the 

 chambers referred to had the office of receiving and retaining 

 supplies of water which should trickle down and keep the gills 

 moist; such was supposed to be an adaptation for the sus- 

 tentation of life out of the water. The experiments of Surgeon 

 Day, however, throw doubt upon this alleged function, and 

 tend to show: (i) that these fishes died when deprived of access 

 to atmospheric air, not from any deleterious properties either 

 in the water or in the apparatus used, but from being unable 

 to subsist on air obtained solely from the water, aerial respira- 

 tion being indispensable; (2) that they can live in moisture 

 out of the water for lengthened periods, and for a short, but 

 variable period in water only ; and (3) that the cavity or recep- 

 tacle does not contain water, but has a moist secreting surface, 

 in which air is retained for the purpose of respiration. It 

 seems probable that the air, after having been supplied for aerial 

 respiration, is ejected by the mouth, and not swallowed to be 



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