XX] SKELETON 509 



the choana or posterior nostril of Amphibia. A further resem- 

 blance to Amphibia is found in the fact that the taste-buds 

 scattered over the body in all other Pisces are in Dipnoi confined 

 to the region of the mouth. The eggs of Protopterus and Lepi- 

 dosiren develop into larvae extraordinarily like the larvae of 

 Amphibia but with four, not three, feathery external gills on each side 

 attached to the gill-arches. Traces of these gills remain through- 

 out life in Protopterus. We see then that Dipnoi present strong 

 resemblances to Amphibia in the anatomy of their "soft parts," 

 and also resemblances to primitive Chondrichthyes, and we shall be 

 disposed to agree with Prof. Kerr that they are nearly related to 

 the old group of fish which first migrated from the seas into the 

 rivers and finally reached swamps liable to dry up, and became in 

 this way ad^)ted to life on land, and so gave rise to all land 

 animals. Strange to say, this conclusion has been attacked by 

 some able zoologists who, basing their conclusions on the skeleton, 

 regard all resemblances between Dipnoi and Amphibia as deceptive. 

 We must therefore turn our attention to the skeleton and see how 

 far these conclusions are justified. 



In the backbone of Dipnoi there are no vertebrae. The noto- 

 chord is surrounded by a thick sheath which as in Chondrichthyes 

 is transformed into cartilage by the invasion of cells derived from 

 the cartilage forming the bases of the neural and haemal arches. 

 These arches are partly transformed into bone, but intercalaries are 

 absent or vestigial and developed irregularly. Neural and haemal 

 arches are ossified. There is a diphycercal fin forming a fringe 

 round the hinder end of the body as in Teleostean larvae and in 

 Amphibian larvae also and there are no separate anal or dorsal fins. 

 The paired fins are of the type called biseriate, i.e. they consist of 

 a jointed axis of pieces of cartilage to which are attached on each 

 side a series of jointed branches termed rays. Such fins have been 

 found in the extinct Osteolepidoti and in the extinct Chondrichthyid 

 P lew acanthus. Such a fin is termed an archipterygium. In 

 Protopterus and Lepidosiren the axis is developed into a long whip- 

 like filament, and the rays are vestigial and attached only to the 

 base of the axis. 



In the skull the upper jaw is completely fused with the cranium, 

 and the teeth in both jaws are amalgamated to form great deutary 

 plates as in Holocephali. Only a pterygoid bone is developed in the 

 upper jaw and premaxilla and maxilla are absent. The cranium 

 is ossified mainly by two great exoccipital bones behind, but 



