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well represented,* * * § its epi- and pharyngo-branchials enormously 
developed and thrown into complex folds, covered with mem- 
brane, which serve to retain a sufficient amount of moisture. 
Sir J. Emerson Tennent describes a remarkable habit which 
some of the Ceylon fishes have of burying themselves in the 
earth, in the dry season, at the bottom of the exhausted ponds, 
there to await the renewal of the water at the change of the 
monsoon — an expedient to which the crocodile also is said to 
resort.f He also states that in those parts of Ceylon where 
the country is flat and small tanks are numerous, the natives 
are accustomed in the hot season to dig in the mud for fish. 
The Cuchia ( Amphipnous ) and the Singio ( Saccobranchus ) 
both fishes of eastern climes, and both extremely tenacious 
of life, also present curious modifications of the branchial 
apparatus, which cannot here be noticed in detail. 
Having considered somewhat at length, on Aristotle’s 
principle of proceeding taro tmv yvcopipcov, the first and more 
general method of water-supply to the gills, not much space is 
left for description of the two remaining processes. 
(3. The respiratory currents enter the mouth and are ex- 
pelled by five orifices on each side.% 
The great bulk of the so-called cartilaginous fishes, namely, the 
sharks and rays,§ afford an instance of this mode of breathing. 
The branchial arches in these fishes, more or less cartilaginous 
in substance, are not hung, so to speak, from below the base of 
the skull, as are those (Fig. 3) of bony fishes, but are attached 
(see Fig. 10) to the sides of the front vertebrae of the trunk. 
Ho branchiostegal or opercular apparatus is functionally present ; 
but from the branchial arches (seen in section in Fig. 9) proceed 
long partitions, or septa, on either side of which are attached 
the gill-plates, || and which form the walls of chambers, or sacs, 
* Hist. Nat. de Poissons, tome vii. pi. 205. The land-crabs, which are 
actually drowned if kept in water, have their gills moistened by the watery 
contents or secretion of a spongy organ situated in the gill-chamber. 
“ The gills of fishes,” as Professor Marshall well observes, “ are not ciliated 
on their surface ; but it is necessary that they should continue moist, or the 
usual respiratory interchanges between the blood and the air dissolved in 
the water would soon cease. Respiration will, however, go on for a short 
time in the air, provided that the gills remain moist.” 
t Ceylon, vol. i. p. 218. In the same volume is given a very interesting 
account of the writings of various ancient authors, e.g. Aristotle and Theo- 
phrastus, on the subject of the Migration of Fishes over Land. 
X The fishes in which this form of respiration occurs were formerly termed 
il pisces branchiis fixis.” 
§ Division Plagiostomi of the order Plasmobranchii (tXacya, a thin plate, 
and (3payx uir , gills). 
I! For the rationale of the arrangement of the gills see the explanation of 
Fig. 11. 
