PROTECTIVE COLORATION. 95 



the brigM-coloured spots on the body, the name of ^olosoma. 

 In two species these spots are bright green in colour, often 

 with a bluish tinge ; in a third species the spots are yellow- 

 green, sometimes almost brown ; while in the remaining two 

 they are orange-brown. I have already suggested the possi- 

 bility of this pigment having a physiological importance ; but 

 it also bears a most striking superficial resemblance to chloro- 

 phyll and to some other plant pigments. The bluish-green 

 colour of the oil globules in ,^. Headleyi recall the bluish 

 green pigments of certain Algse, and the other colours recall 

 pigments of an almost identical hue in other plants, though 

 apparently they have no chemical relationship to them what- 

 ever. As the bodies of these small worms are transparent, 

 they present no small resemblance to a living or dead (with the 

 chlorophyll altered) filament of an Alga. But we can hardly 

 suppose that this resemblance is of much use to the worm 

 which is preyed upon by animals that cannot have the least 

 appreciation of its colours. 



Protective Coloration in Man. 

 It is even said that man himself may assimilate in colour to 

 his surroundings. The traveller Schweinfurth remarks that 

 " the Bongos have a reddish-brown skin similar in colour to 

 the soil of their country; the Diuhas (a neighbouring race), on 

 the other hand, are as black as the alluvium of their native 

 soil." It should be added, however, that Dr. Schweinfurth 

 instances this fact rather as a curious accident than as an 

 example tending to prove the truth of any theory respecting 

 protective resemblance. 



Green Colour of the SlotL 



The greenish colour of the hair of the sloth is very sug- 

 gestive of a lichen-covered branch ; and, considering the 



