98 FISH GALLERY. 



28.] of a triple division. Along the middle of the fin runs a jointed 

 axis, the joints gradually becoming smaller and thinner towards the 

 extremity ; each joint bears on each side a three-, two-, or one- 

 jointed branch. This " axial" arrangement, which evidently 

 represents one of the first and lowest conditions of the skeleton of 

 the limb of Vertebrates, is found in Ceratodus with the branches, 

 but in Lepidosiren the jointed axis only has been preserved, with 

 the addition of rudimentary rays in Protopterus. 



Three recent genera and four species are known, viz.: Lepidosiren 

 paradoxa (fig. 88), from the Amazons and Paraguay ; Protopterus 



Fig. 88. 



i-en pamdoxa. (From South America.) 



annectens, spread over the whole of tropical Africa; and Ceratodus, 

 from the fresh waters of Queensland, with two species, C. forsteri and 

 C. miolepis. Protopterus lives in shallow waters which periodically 

 dry up. During the dry season they form a cavity in the mud, the 

 inside of which is lined with a capsule of mucus, and from which they 

 emerge again when the rains refill the pools inhabited by them. The 

 balls of clay containing the fishes in a torpid condition are sometimes 

 brought to Europe, and some are exhibited here. Lepidosiren has 



