60 FISH GALLERY. 



DIPNEUMONES. 



Proto- I n the Dipneumones, including the African Lung-fishes, 



pterus. Protopterus, 174, 175, 176, and the American Lung-fish, Lepido- 

 siren, 173, the lungs are two in number, but they communicate 

 with the oesophagus by a single opening. The gill system is 

 more reduced than in Ceratodus, for whereas in that fish four gill- 

 arches bear gills, in the Dipneumones the first and second arches 

 have no gills. In the young there are one or more external gills, 

 projecting freely, and situated above the gill-opening. These have 

 a thick central axis and a fringe, and bear some resemblance to 

 the fins, so much so that some authorities regard the paired limbs 

 of Vertebrates as having been derived by a modification of gill 

 structures, Occasionally the external gills persist, in a reduced 

 form, in adult life. As in Ceratodus the tail is reduced and 

 symmetrical, and is continuous with the single, undivided dorsal 

 and anal fins, but the paired fins differ in being more slender and 

 in not possessing the fringe along the front edge. 



The genus Protopterus has a wide distribution over the 

 continent of Africa, and three species are to be distinguished. 

 The fishes are found in marshes in the vicinity of rivers ; they are 

 mainly carnivorous and voracious, and their food consists of frogs, 

 worms and insects. The three species differ in the length of the 

 head, the number of scales in the lateral line, the size of the eyes, 

 and the position of the front end of the dorsal fin. The Gambian 

 Lung-fish, Protopterus annectens, 176, has been longest known, 

 the larger species, the Egyptian Lung-fish, Protopterus cethiopicus, 

 175, and the Congo Lung-fish, Protopterus dolloi, 174<, are 

 comparatively recent discoveries (fig. 35). 



At the beginning of the dry season the Protopterus buries itself 

 in the thick mud of the swamps in which it lives, and remains 

 curled up in a dormant condition for several months. An opening 

 is left at the upper end of the mud chamber for breathiug purposes^ 

 respiration during the dry season being effected by the lungs alone. 

 The two dried nodules of clay exhibited (178) contain each a small 

 specimen (now shrivelled up) of Protopterus annectens. 

 Lepido- In the South American Lung-fish, Lepido sir en paradox a (173, 



and fig. 35), the body is long and rounded, and the paired fins 



siren. 



