THE TELEOSTEI. 141 



face of the respiratory mucous membrane do not reach the 

 outer edges of these septa. 



In Chiinmra, the free edges of the septa are exceedingly 

 narrow, and the apices of the branchial processes extend out- 

 ward to them. 



In the Sturgeon, the septum is not more than three-fourths 

 a» long as the branchial processes, the apices of which are 

 oonsequently free. 



The process of reduction is carried still further in the lele- 

 Ostei — the septum not attaining to more than one-third the 

 length of the branchial processes ; and, as in the Ganoids, 

 each process is supported by an osseous or cartilaginous 

 skeleton. 



The Teleostei have no functional hyoidean, or opercular, 

 gill ; and, as a general rule, each of their four branchial arches 

 possesses a double series of branchial processes, making eight 

 in all. Not unfrequently ( Cottus, Cydopterun, Zeus, etc.), the 

 number is reduced to seven ; the fourth branchial arch having 

 only one series, the anterior. In this case, the gill-cleft, which 

 should lie between this arch and the fifth, is closed. Some- 

 times there are only six series of branchial processes, the fourth 

 arch being devoid of any (e. g., Lophius, Diodon). In Hal- 

 thma the number is reduced to five, only the anterior series of 

 the third arch being developed; and in Amphipnous cuchia 

 only the second branchial arch possesses branchial filaments, 

 the first, third, and fourth, being devoid of them. 



Many Teleostean fishes possess accessory respiratory or- 

 gans. These may take the form of arborescent appendages to 

 the upper ends of some of the branchial arches, as in Clarias, 

 Seterobranchus, and Seterotis ; or, as in the Climbing Perch 

 (^Anabas) and its allies, the epipharyngeal bones may enlarge 

 and acquire a labyrinthic honeycombed structure, and support 

 a large surface of vascular mucous membrane ; or, as in the Clu- 

 peoid {Lutodeira chanos), an accessory gill may be developed 

 in a curved csecal prolongation of the branchial cavity. Final- 

 ly, in iSaccoh'anchits singio and in Amphipnous cuchia, the 

 membrane lining the branchial chamber is prolonged into sacs, 

 which lie at the sides of the body, and receive the blood from 

 the divisions of the cardiac aorta which supply the branchise, 

 while they return it into the dorsal aorta. 



All these fishes (except Lutodeira) are remarkable for their 

 pow^er of sustaining life out of the water. Manj' inhabit the 

 marshes of hot countries, which become more or less desic- 

 cated in tlie dry season. 



