VASCULAR SYSTEM OF FISHES. 267 



Ganges {Monopterus, Si/mbranc/ms)* ; it is persistent in the first and 

 second branchial arches of the eel -like Lepidosiren (Jf(/. 71, 2, 3). 

 Such arches are, therefore, gill-less, and a certain proportion only of 

 the blood transmitted from the heart is aerated in the gills : about 

 one fourth, e. g. in Monopterus, goes direct to the aorta in its venous 

 state ; a larger quantity would pass into the roots of the aorta 

 (ib. o, o), and mix with the general circulation in the Lepidosiren, 

 were no part of the current diverted by the vessels /, V, into the lung- 

 like modification of its air-bladder. 



The Hunterian specimens, Nos. 3255. and 3260. show the external 

 branchial filaments in the embryos of a Dog-fish and Shai'k ; three 

 such filaments are retained on each side, for a long period, in the 

 Lepidosiren annectens. Accessory respiratory organs, analogous to, 

 if not homologous with, the opercular gills, 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 

 highly vascular membrane supported on singular sinuous plates de- 

 veloped from tlie epibranchials of tlic anterior branchial arches (Jfg. 39. 

 48) ; whence this family of fishes is called Lahyrinthihranchii. An 

 accessory branchial ramified vascular organ is similarly situated in 

 the genus thence called Heterobranchus. From the rich vascularity 

 of these organs they resemble miniature trees of red coral ; they are 

 holloAV and muscular, serving not only for respiration, but, as Cuvier 

 suggests, to aid in propelling the arterialised blood into the aorta. lu 

 the Cuchia (Amphijmons), 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 func- 

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

 branchial arches, covered by the upper part of the opercular mcjnbrane ; 

 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 rudimental gills. Those from the su])plenu'ntal lung-like 

 vascular sacs arc collected into two trunks, wliicli 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 

 conveyed 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 liumo- 

 logues of the superior branchial sacs extend in a Gangetic Siluroid 



* Taylor, cxvii. 



