xlviii RESPIRATION. 



page 72) there are three gills, in the curious tropical Malthe belonging 

 to the same family the Pediculati, two and a half, while the eel-like 

 and amphibious Cuchia of Asia has merely one small gill belonging 

 to the second branchial arch. The pharyngeal or inner side of these 

 gill-arches may be simply covered with integument or possess projections 

 of varying forms which have been designated gill-rakers, and whose numbers 

 sometimes assist in ascertaining the distinction between two nearly 

 allied species as in. our two common sh'ads (vol. ii, pp. 234, 236).' 

 These gill-rakers may be very fine, long, placed close together, and per- 

 forming the function of a sieve by arresting the progress of anything but 

 water from the pharynx to the gills. Or they may be placed somewhat 

 wider asunder, be shorter in length, and then would be only efficacious in 

 stopping , large particles. In some forms they may be teeth-bearing 

 tubercles, or simply rough. Irrespective of this sieve-like apparatus pre- 

 venting foreign bodies passing from the pharynx through the clefts or 

 slits existing between the branchial or gill-arches to the gills, their inter- 

 branchial slits may be decreased in size, or even obliterated ; for in some 

 forms, as in Cottus, no opening or slit is to be found behind the fourth 

 branchial arch, and when this is the case merely a single or uniserial gill is 

 present on it. 



The gills or branchiae of fishes may be destitute of support as among the 

 Plagiostomata (vol. ii, page 287), or be supported by horny or cartilaginous 

 processes placed along the outer convex edge of the branchial or gill- 

 arches and fixed in the integment. Normally or in complete gills there are 

 two rows of these rods, one along either edge, whereas in the uniserial or 

 half-gills there only exists one row. Although all gills are essentially the 

 same as to their formation, their appearance differs, thus among the Lopho- 

 branchiate forms (vol. ii, page 256) each gill expands towards its free 

 ' extremity, whereas they generally become attenuated and compressed, while 

 numerous varieties are observable. 



The pseudobranchiae, or false gills, which often exist, are situated more 

 along the inner side of the gill-covers in teleosteans, or within the spiracles 

 in Chondropterygians, or concealed under the integument so as to appear 

 like a glandular body on the remains of an anterior gill which in the 

 embryonic life of the fish .performed respiratory functions, but which in the 

 adult fish receives arterial blood. 



Accessory respiratory organs exist in some fishes, especially tropical 

 forms, as in the climbing perch among the Labyrinthici, the walking fishes 

 among the Ophiocephalidse, and the scorpion-fish Saccobranchus and the 

 Clarias among siluroids or sheat-fishes. Joubert remarks that respiration 

 • may be carried on in Gallichthys by air passing through the intestines ; in 

 Boras, Erythrinus, and Sardis gigas, the air-bladder performs this function. 



