no. 1881. NEW TROPICAL MILLIPEDS— COOK. 453 



the animal gains not merely a protective coloration, like the surround- 

 ing soil, but a firmly attached coating of the actual soil material. 



From the evolutionary standpoint the hairy covering that holds 

 the soil particles may be considered as an adaptive character of the 

 same general class as protective colorations and mimetic resemblances. 

 It certainly renders the earth-covered animals much more difficult to 

 collect for scientific purposes than members of other families with 

 clean surfaces. An experiment with one of these earth-covered types 

 (Stylodesmus) in Liberia showed that the unpracticed eye could detect 

 the creatures only with great difficulty against their natural back- 

 ground of earth, even after the location of the specimens had been 

 quite definitely pointed out. After my friends had been told how 

 many specimens were under a particular leaf they often took several 

 minutes to find them. 



Yet there is nothing to indicate that other families of millipeds have 

 suffered any evolutionary advantage or disadvantage from the lack 

 of the protective covering. There is a very wide range of colors and 

 combinations. Some are black, some white, some with inconspicuous 

 grays and browns. Bright yellows, reds, purples, and even blue 

 shades, are also found that might be considered as sexual attractions 

 or warnings to enemies, were it not for the fact that the animals are 

 all completely eyeless and nocturnal in their habits. 



The new Porto Rican milliped * is of interest quite apart from the 

 question of the protective value of the earthy covering, which it 

 shares with many related genera. If natural selection by external 

 agencies were needed to bring about changes of characters, no further 

 evolution of the dorsal surfaces of these hairy earth-covered millipeds 

 would be expected after the object of protective coloration had been 

 so perfectly attained. Different environments could make no new 

 demands for more adequate protection, for in this respect the creatures 

 are equally well adapted for every environment in which their other 

 limitations would enable them to exist. They can assume com- 

 pletely the color and texture of any kind of soil in which they may 

 happen to live. And yet evolution has continued to go on underneath 

 this covering of earth. 



It seems impossible to imagine that any use can attach to the 

 elaborate and highly specialized lobing of the margins of the segments, 

 the peculiarity that distinguishes the new Porto Rican milliped from 

 the two closely related West Indian genera, Tridesmus and Docodes- 

 mus. For animals with naked surfaces such lobing would involve a 

 practical change in the outlines of the segments and the general 

 appearance of the body, that might be of significance in relation to 

 the external environment, but in the actual case extensive changes 



» See p. 465. 



