FEOM THALES TO LAMARCK 17 



and crocodiles possess very strongly developed front and hind 

 legs. In the long thin Skinks (Chalcides) only four feet-stumps 

 are developed which have no functions. Reversion has gone 

 still further in the blind-worms, which are even without external 

 vestiges of extremities, whilst finally in the snakes not only the 

 extremities themselves, but also their connections with the ver- 

 tebral column, shoulder, and pelvic girdle have been lost. Only 

 the pythons and boas still possess rudiments (Arilagen) of a 

 pelvis and the hind extremities ; these are, however, no longer 

 preserved as means of locomotion, but for purposes of copula- 

 tion. It is interesting to note that in the snakes the want of 

 extremities is not only balanced by the enormous elongation of 

 the body, but also of the ribs, which, having become free and 

 movable, are made to assist in locomotion. This law does not 

 even fail in the highest vertebrates, the mammals, for it is well 

 known that, for instance, monkeys with very long tails possess 

 proportionally weaker arms and legs than the short-tailed or 

 tailless baboons and anthropoid apes. 



But let us return to the fishes. One of the quaintest among 

 them, a veritable clown among fishes, is the African Mud- 

 jumper (Periophthalmus koelreuteri) (fig. 3). It is found all 

 along the West Coast of Africa, but varies according to its habitat 

 in colour and marking. It is usually greyish-green or brown ? 

 with silver spots and stripes. The fins are blue, the very 

 prominent eyes red. Its length does not exceed 15 cm. Its 

 life-habits are more those of a newt or frog than of a fish, 

 for it feels both at home in the water and out of it. At ebb- 

 tide one may see them in tribes of dozens, lying on the wet sand 

 in numerous parts of the West African coast, or moving along by 

 means of curious short jumps. Because of their temporary 

 sojourn on the land the pectoral fins of the Mud-jumper have 

 assumed a leg-like appearance and are used even for climbing, 

 for they may frequently be seen ascending the air-roots of man- 

 grove trees on which they hold their siesta. Still more wonderful 

 than the change of their fins into instruments of walking and 

 climbing is the adaptation of their respiratory organs to a life in 

 the air. We know how sensitive most fishes are to want of 

 water and how soon they perish when removed from their proper 

 element. But the Mud-jumper is able to loaf about on the land 



2 



