CHAPTER XXI 
LABYRINTHICI AND HOLCONOTI. 
is the group of Labyrinthicit, composed of perch-like 
ys| 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: (1) 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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