GILLS OF FISHES. 487 



respiratory character before they are absorbed. Accessory 

 respiratory organs, acting chiefly as a reservoir or filter of 

 water, 1 are developed from the upper part of the pharynx 

 in the Climbing Perch (Anabas scandens) and allied fishes of 

 amphibious habits ; they are complex folds of slightly vascular 

 membrane supported on sinuous plates developed from the 

 pharyngo- and epi-branchials of the ante- 325 



rior branchial arches, fig. 325, 48 ; whence 

 this family of fishes is called Labyrinthi- 

 branchii. An accessory branchial ramified 

 vascular or'an is similarly situated in the 



~ > 



genus thence called Heterobranchus. It re- 

 sembles a miniature tree of red coral, is 

 hollow and muscular, and serves not only for 

 respiration, but, as Cuvier suggests, to aid in 



propelling the arterialised blood intO the Branchial arches and labyrin- 



.1 r* ^ ft 7 \ tbic reservoir, Anabas. xxiri. 



aorta. In the Lucnia (Amp/upnous), a 



finless snake-like fish, which lurks in holes in the marshes of 

 Bengal, the second branchial arch supports a few long fibrils, and 

 the third a simple lamina fringed at its edge ; the first and fourth 

 arches have not even the rudiment of a gill. The branchial 

 function is transferred to a receptacle on each side of the head, 

 above the branchial arches, covered by the upper part of the oper- 

 cular membrane ; these receptacles have a cellular and highly 

 vascular internal surface ; the cavity communicates with the 

 mouth by an opening between the hyoid and first branchial arch, 

 and receives its blood from the terminal bifurcation of the 

 branchial artery, and also from the efferent vessels of the rudi- 

 mental gills. Those from the supplemental lung-like vascular 

 sacs are collected into two trunks, which unite with the posterior 

 unbranched branchial arteries to form the aorta. Thus about one 

 half of the volume of blood transmitted from the heart is con- 

 veyed to the aorta without being exposed to the action of the air. 

 This amphibious fish is, as might be expected, of a sluggish and 

 torpid nature, and remarkable for its tenacity of life. The homo- 

 logues of the superior branchial sacs extend in a Gangetic Siluroid 

 fish, the Singio, beyond the cranium, backward beneath the dorsal 

 myocommata upon the neural arches of the vertebra? to near the 

 end of the tail, where they terminate in blind ends. The inner 

 tunic of the sacs is a delicate vascular membrane, supplied by a 

 continuation of the posterior branchial artery. The position of 

 the palatal opening of the sac, in relation to the lamina? of the 



1 CLXXIV, vol. iii. p. 372. 



