174 DARWINISM TO-DAY. 



escape the same dangers in the struggle for existence by 

 means of different means. And by this the probability is 

 made greater that the 'needed variation' appears at the 

 right time. The differing characteristics of this sort will 

 later lead, through crossing, to the formation of a mixed 

 type, or, if the competition grows ever sharper with the 

 course of time, they will produce a separation of the species 

 into varieties (eventually species) with differing habits of 

 life, or finally they may meet in direct competition or strug- 

 gle with one another. The good flyers among the birds all 

 have long wings, but in some it is the fore arm which is 

 specially lengthened (cuckoo, goat-sucker, pigeon), in others 

 the hand (terns, humming-birds, eave swallows), and in 

 still others the upper arm (swan). While Tapirns ameri- 

 canus, like most mammals, drives the flies away from its 

 eyes by throwing down the eyelids, Tapirus indicus accom- 

 plishes the same thing by a strong rotation of the bulb of 

 the eye. Elcphas africanus seizes very small objects with 

 its proboscis-fingers, while the Indian elephant lays the front 

 end of the trunk laterally on the ground, grasps the object 

 between the skin-folds, lifts it up high in this way, and 

 only then allows it to fall into the tip of the proboscis. 

 Poulton has shown by several examples that in cases of 

 mimicry the same effects may be got in very different ways. 

 The glass-like transparency of the wings, for example, is got 

 in the Heliconid genus Mcnthona by a considerable dimi- 

 nution in size of the scales, in the Danaid I tuna iliona through 

 the absence of most of the scales, in Castnia linus var. hcli- 

 conoides, through the absence of pigment in the scales, which 

 are as large and numerous as usual, in the Pierid Dismor- 

 phia crise through the smallness of the scales, and finally in 

 the night moth Hyelosia heliconoides by the absence of pig- 

 ment and lessened number of the scales." 



Plate next offers a detailed explanation on strict Darwin- 

 ian grounds of how such an extraordinary condition of 



