84 THE FOUNDATIONS OF ZOOLOGY 



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poison of serpents, mings which are useful only in their effect 

 on other animals than the user ? 



How are we to explain adjustments to the life of other beings 

 than the ones that exhibit the adjustment? 



As the serpent which is able to destroy its prey, and the bee 

 which is able to drive away its enemies, have an advantage in the 

 struggle for existence, it is easy to understand how these powers may 

 have arisen through selection ; for the bee's sting is a modified ovi- 

 positor, and it is used by some of the Hymenoptera both as a 

 weapon of defence, and as an organ for laying the eggs in the 

 tissues of plants, thus exciting pathological changes in these tissues, 

 so that they form galls, and store up, around the eggs, starch to 

 serve as food for the larvae which hatch from the eggs. While the 

 origin of these adjustments by selection is quite intelligible, there 

 does not seem to be any other way to account for them. 



The white upturned tail of the rabbit is a danger-signal. When 

 disturbed or alarmed on the feeding-ground, which they visit soon 

 after sunset or on moonlight nights, the rabbits make for their 

 burrows, and the white upturned tails of those in front serve as 

 guides and signals to those more remote from home, to the young 

 and feeble ; and thus, each following the one or two before it, all 

 are able, with the least possible delay, to reach a place of safety. 



Many defenceless insects are protected by their resemblance to 

 dangerous animals, or by some threatening or unusual appearance. 

 The great green caterpillar, known in some of our Southern states 

 as the "hickory-horned devil," has an immense crown of orange- 

 red tentacles, which, if disturbed, it erects and shakes from side 

 to side in a manner so alarming that the negroes believe it is 

 more deadly than a rattlesnake. 



Who can believe that the inherited effect of the terror it excites 

 has modified the hickory-horned devil? After giving the matter 

 my best and most serious thought, I am unable to imagine any way 

 in which the effect of the upturned tail of the hinder rabbit can act 

 upon the tail of the rabbit in front, or any way by which the sight 

 of the tail in front can modify the tail of the rabbit behind. I find 

 the production of adaptations of this sort by the inheritance of 

 the beneficial effects of use, or in any way except by selection, quite 

 unthinkable. Most pelagic larvae are transparent, even when the 



