108 



VERTEBRATE ZOOLOGY 



ectodermal epithelium of the branchial clefts. They are foimd in the 



embrybs of many elasmobranchs (Fig. 57) and in some teleosts. A 



notable case of larval gills is seen in the advanced larva of Polyp- 



terus (Fig. 70, C). 



Internal gills are true functional gills of adult fishes. They are finely 



divided diverticula of the endodermal epithehum of the branchial 



clefts. Their location is well shown in the diagrams of elasmobranch 



and teleost heads (Fig. 58). 



The Air-bladder and Accbs- 



*5e. ^■^ ^-r-r770v"i SCRY Organs of Respiration 



In all of the groups of fishes 

 above the elasmobranchs there is 

 a single or paired air-bladder, a 

 sac-like diverticulum of the phar- 

 ynx derived from either dorsal or 

 ventral sides of the alimentary 

 tract. It is in all cases supplied 

 Fig. 59.-Respiratory labyrinth „f ^^th bk)od from the "pulmonary 

 the Climbing Perch (Anabas scandens) artery and, primitively at least, 

 exposed by removal of part of operculum, subserves two functions: that of 

 ffnl^''* branchial arch; lo, labyrinth- a hydrostatic or buoyancy organ 

 itorm organ; op, operculum, she, supra^ ^ j.u j. c J J b 



branchial cavity. (From Bridge). ^^^ ''"a* °I ^^ accessory respira- 



tory organ or primitive lung. In 



Fig. 60 -Accessory respiratory organs of the cat-fish, Clarias, as seen after 

 removal of operculum, a, anterior arborescent organ; b. a ^-\ first four branchial 

 arches, d.b. c, dorsal extension of left branchial cavity;/, modified «ill-filaments: 

 op, base of operculum; p, posterior arborescent organ. (From Bridge ) 



