986 



PISCES. 



so retained in contact with the branchiae con- 

 tinually absorbing from the air a sufficiency of 

 oxygen to carry on the respiratory process. 



An important group of Fishes (the " P/ia- 

 ryngiens labyrint/iiformes" of Cuv.) are cha- 

 racterized by a very peculiar formation of the 

 anterior superior pharyngeal bones, which 

 enables them to live out of the water for a 

 considerable length of time, so that many of 

 them, as we are assured by authors, not un- 

 frequently come on dry land, and even, as in 

 the case of the Anabas scandens, or climbing 

 Perch, mount into trees, a faculty for which 

 they are indebted to the following remarkable 

 conformation. 



Their inferior pharyngeals and the posterior 

 of their superior pharyngeal bones present the 

 usual arrangement and are studded with teeth, 

 but the two anterior pharyngeals on each side 

 are spread out into thin laminae folded upon 

 themselves in divers ways, so as to form a light 

 complicated mass, (which Cuvier* compares to 

 a curly cabbage, or to certain forms of lami- 

 nated eschars and millepores,) over which 

 numerous vessels are distributed, but whether 

 derived from the branchial artery or the aorta 

 remains uncertain. In order to lodge these 

 singular cellular organs the head is consider- 

 ably dilated in breadth, and with the same 

 intention the cranium is produced upwards by 

 a vertical crest so as to increase the height of 

 the lateral chambers in which the foliaceous 

 masses are lodged. Externally, each of these 

 chambers is partially covered by the bones of 

 the cranium and by the opercular pieces ; and 

 when the operculum is raised, a membrane is 

 seen to be tightly expanded between it and the 

 opercular bone so as to enclose the cavity, 

 leaving only a small aperture of communica- 

 tion with the exterior, which leads equally to 

 the labyrinthiform apparatus and the branchial 

 chamber. This bony labyrinth, therefore, so 

 carefully enclosed on all sides, and which re- 

 ceives water equally with the branchiae when- 

 ever the fish opens its mouth, will retain the 

 water so taken in between its lamellae where- 

 with to moisten the branchiae for a considerable 

 length of time, so that the fish may live for 

 hours or perhaps even for days out of the 

 water. 



The Lophobranchii form a remarkable group, 

 distinguished from all other races of osseous 

 Fishes by the peculiar structure of their bran- 

 chial organs. In these, called from their pecu- 

 liar shapes and external armour " pipe-fishes," 

 ( Syngnatlnis, Hippocampus, fyc.) the vascular 

 fringes appended to the branchial arches, in- 

 stead of consisting of lamellae arranged in a 

 pectinated form, are collected into tufts ar- 

 ranged in a double series along the convexity 

 of each branchial arch. The essential character 

 of these tufts varies, however, in no respect 

 from that of gills of the ordinary construction, 

 and in like manner the water passes from the 

 mouth through five apertures leading from the 

 pharynx into the branchial chamber, whence, 



* Hist. Acs Poissons, torn. 8. 



after bathing the tufted gills, it escapes through 

 a single small opercular fissure. 



The Sturgeons (Sturionida), which in many 

 points of their economy seem intermediate be- 

 tween the osseous and cartilaginous Fishes, 

 resemble the former in the disposition of their 

 organs of respiration. The gills of the Stur- 

 geon are constructed precisely in the same 

 manner as in ordinary osseous Fishes, only 

 differing in some respects as to form, the bran- 

 chial arches being more bent and the vascular 

 laminae united for a greater extent; the respired 

 water, moreover, escapes in like manner through 

 a single opercular slit. 



In the Plagiostome cartilaginous Fishes 

 (" Chondropterygii a branchies fixes," Cuv.) 

 the mechanical arrangement of the branchial 

 organs presents very important modifications, 

 the water which passes from the mouth over 

 the gills no longer escaping through an oper- 

 cular opening, but being expelled through five 

 distinct orifices situated on each side of the 

 body. In the Sharks and Rays the condition of 

 the breathing organs is essentially similar, so 

 that the same description will apply to both. 

 The four branchial arches in these Fishes are 

 of a soft cartilaginous consistence, and instead 

 of hanging free in the branchial chamber as 

 they do in the osseous genera, stretch quite 

 across that cavity to have their external margins 

 fixed to its outer walls, thus dividing it like so 

 many bulk-heads into five distinct compart- 

 ments, which have no communication with 

 each other. A wide branchial fissure admits 

 water from the pharynx into each of these com- 

 partments, which after passing over the gills is 

 expelled by as many orifices situated upon the 

 exterior of the body, the external openings 

 being situated upon the sides of the throat in 

 theSqualidae (Jig. 506, q, q,q\ but in the Skate?, 

 in consequence of the lateral extension of the 

 body, they are placed upon the ventral surface. 

 The gills themselves are broad vascular mem- 

 branes spread out over the opposite faces of each 

 cartilaginous septum, so that every compartment 

 of the branchial chamber has its walls tapes- 

 tried with a respiratory surface, and forms a 

 kind of bag lined with innumerable blood- 

 vessels, through which the water must pass in 

 its course from the mouth to the external open- 

 ings upon the sides of the neck. 



The branchial membrane which thus covers 

 the opposed walls that bound the respective 

 cavities into which the gill-chamber is divided, 

 is entirely made up of numerous plicated, vas- 

 cular lamellae, each of which is gathered into 

 close-set transverse folds sustaining the minute 

 ramifications of the branchial vessels; and these 

 again may be observed with a lens to be in like 

 manner transversely plicated, thus presenting 

 in the aggregate a surface of vast extent to the 

 influence of the respiratory currents. In the 

 anterior branchia the vascular layer is of course 

 affixed only to the posterior surface of the sup- 

 porting membrane, the opposite side being sup- 

 ported by cartilaginous rays.* 



* Monro makes the following calculation rela- 



