THE FACTORS OF EVOLUTION 165 



surprise. We can here distinguish two forms of imitation. 

 Some animals possess an astonishing likeness to dead objects 

 dried twigs, leaves, etc. ; others again assume the exact shape 

 and appearance of a distantly related species. Phyllopteryx 

 eques, a fish of the Australian seas, strikingly resembles, with its 

 bizarre, ragged, ribbon-like body-appendices, the seaweed in 

 which it lives and with which its colour harmonizes. Many 

 looper-caterpillars (Geometridce} look like dry twigs, several 

 little beetles and loopers like the dejecta of birds. Xylina 

 vetusta in a resting position looks like a piece of dried wood- 

 Striking instances of protective mimicry are found among 

 the Phasmids. Every one knows the so-called Walking-leaf 

 (Phyllium siccifolium), which, in its colour as well as the form 

 of its body, legs and wings, looks exactly like a green leaf. 

 We frequently find in butterflies for instance, in the Death's- 

 head moth, the ' red underwings,' etc. that in a resting position 

 they mimic the dry bark or leaves of trees, while during 

 flight they exhibit brilliant colours. Because the day butterflies 

 fold both pairs of wings over the back, but the ' owls ' place the 

 upper wings over the underwings, in the former the whole lower 

 side, in the others only the upper side of the wings is furnished 

 with protective colours and designs. Probably the most beau- 

 tiful instance is the famous Kallima, a tropical butterfly, which 

 in a resting position looks exactly like a dried leaf. 



Equally general is mimicry proper, that is, the mimicking of 

 one species of animal by another species. In these cases the 

 mimicked species is usually one which has little to fear 

 from natural enemies by reason of its venom, its objectionable 

 taste, etc., while the mimicker is unarmed and exposed to 

 numerous attacks. Thus the hornet with its dreaded poison 

 dart is mimicked by the harmless hornet-moth ; humble-bees 

 and honey-bees serve as a ' model ' for various species of flies ; 

 wasps are mimicked by beetles, and ants by spiders. In the 

 forests of Guatemala lives the coral-snake (Elaps corallinus), 

 dreaded on account of its fatal venom, a strikingly beautiful 

 animal whose brilliant red body with black transverse bands 

 is conspicuous afar. In social union with it lives a harmless 

 snake of another genus, Erythrolampsus, which resembles the 

 coral-snake in all details so much that only an expert is able to 



