156 



MEANING OF THE SYSTEM. 



live. For example, amongst the butterflies certain Leptalidce resemble 

 in outward appearance and in mode of flight a species of the family 

 Heliconius (fig. 116), which appears to be protected from the pursuit 

 of birds and lizards by a yellow disagreeable-smelling fluid, and 

 share the same locality with the above-mentioned species. The 

 most perfect instances of mimicry are found in the Tropics of the 

 Old World, where the Danaidce and Acrceidce are imitated by the 

 Papilionidse (Danais niavius, Pajnlio liippocoon Danais echeria, 

 Papilio cenea Acrcea yea y Panopcea hirce). Cases of mimicry fre- 

 quently occur between insects of different orders ; butterflies imitate 

 the form of Hymenoptera, which are protected by the possession of 

 spines (Sesia bombyliformis Bombus hortorum, etc.) In the same way 



certain beetles resemble bees 

 and wasps (Charis melipona, 

 Odontocera odyneroides), and 

 the Orthopteran genus Con- 

 dylodera tricondyloides from 

 the Philippines is like a genus 

 of Cicindelff (Tricondyla\ 

 Numerous Diptera have the 

 form and colour of stinging 

 tiphegidw and Wasps. Also 

 among Vertebrates (Serpents 

 and Birds) some examples of 

 mimicry are known. 



Evidence from Rudimen- 

 tary Organs, Rudimentary 

 organs, too, which are so 

 common, are satisfactorily ex- 

 plained by the theory of selec- 

 tion as the result of non- 

 employment of such organs. Organs which were formerly functional 

 have gradually or even suddenly become functionless as a result of 

 adaptation to special conditions of life, and, through want of exercise, 

 have, after the lapse of generations, become weaker and finally aborted 

 or degraded (Parasites). We cannot, however, assert that rudimentary 

 organs -are in all cases useless. They have, on the contrary, often 

 gained secondary functions, though this may be difficult to demon- 

 strate. 



We find, for instance, in certain snakes (Pt/thonidcv) that there 

 are small processes armed with claws at the sides of the anus (anal 



FIG. 116. u, Leptalis Theonoe, var. Leitconoi; 

 (Pieris). I, Ithoiiiiu Ilerdina (the mimicked 

 Heliconius). (After Bates.) 



