MIMICRY IN SPIDERS. 359 



cordially adopts the opinion expressed by Mr. Bates concerning the remark- 

 able mimicry between the genera of butterflies, Ithomia and Leptalis, as they 

 are found in Brazil.' Mr. Bates concludes that the Leptalis first varies, 

 and when tliat variety happens to resemble in some degree any common 

 butterfly iidiabiting the same district, this variety, from its resemblance to 

 a flourishing and little persecuted kind, has a better chance of escaping 

 destruction from predaccous birds and insects, and is consequently oftener 

 preserved, the less perfect degrees of resemblance being from generation to 

 generation eliminated, and oidy the others left to propagate the kind. 



In this connection Mr. Darwin remarks: "Insects cannot escape by 

 flight from the larger animals, licncc they are reduced, like most weak 

 creatures, to trickery and dissimulation."^ In what sense can it be true 

 that a resemblance in form, which must be the result of influences oper- 

 ating upon the very germ of life, acquired by and transmitted from an- 

 cestors, is traceable to the volition of the creature, and is an act of delib- 

 erate "dissimulation and trickery"? Whatever may have been the origin 

 of adaptive resemblances, certainly at the outset we may exclude any such 

 supposition as this. In the nature of things the cause of structural re- 

 semblance is beyond the individual control of the mocking or mimicking 

 species. 



The most striking example of the mimicry of animal forms among 

 spiders, as has been said, is that of Ant spiders, of which Siraonella ameri- 

 cana is an example. The theory which accounts for this on the 

 Anthke ]^ypoti,esJs of natural selection supposes that, through the nat- 

 Porms. ^^^^ tendency to vary, a spider in a brood accjuired a slight re- 

 semblance to an ant. This sliglit resemblance protected the spiderling so 

 much as to give it an advantage over its fellows during the attacks of 

 birds that feed upon spiders, but do not feed upon ants. This protected 

 individual, having matured, transmitted its peculiarity to offspring, some 

 of whom, by the same tendency to variation, exaggerated the ant likeness; 

 and so, by infinitesimal increments, in the course of time Simonella amer- 

 icana and other species more or less closely resembling ants were produced. 



Concerning this theory it may be remarked, first, that the real difficulty 



seems to be in the supposition that such a slight variation as is supposed 



could possibly be of any advantage to an individual spiderling 



Value of jn the midst of a large brood. The dangers to which these are 



f}^^^\. exiwsed are not chiefly from birds. They are very small, soft 



Variation '■ , -i a ii, j. 



bodied creatures, exposed to many perils. As soon as they set 



up housekeeping, and even before it, they are preyed upon by their own 



order, for large spiders unceremoniously eat little ones, and small spiders 



eat less ones. Among , Wanderers like Sunonella and other Attidaj, the 



/ 



' Bates/" Naturalist on the Amazon." 



2 "Oriy.in of Species," Chapter XIII., page 38(i. 



N 



