26 COSMIC PHILOSOPHY. [ft. n. 



and ground-beetles emit a disagreeable, pungent smell, and 

 they are often conspicuously coloured. But the most 

 wonderful of all are the cases of protective mimicry. The 

 heliconidse are among the most beautiful of South American 

 butterflies. Being never eaten by birds, on account of a 

 nauseous liquid which exudes from them when touched, they 

 are not only very lazy Byers, but have the under sides of their 

 wings as gorgeously tinted as the upper side, so that they 

 can be seen from quite a "ong distance. From the same 

 cause they are prodigiously numerous, swarming in all the 

 tropical forests. Now it is obvious that if another butterfly, 

 not protected by a disagreeable odour or taste, were to 

 resemble the heliconia in colouring, it would be as efficiently 

 protected as by imitating a dead leaf or dry twig ; provided 

 that there were but few of these butterflies among a large 

 number of heliconias. For, as Mr. Wallace says, "if the 

 birds could not distinguish the two kinds externally, and there 

 were on the average only one eatable among fifty uneatable, 

 they would soon give up seeking for the eatable ones, even if 

 they knew them to exist." Xow along with the heliconidse 

 there does, in fact, live a distinct family of butterflies, the 

 pieridse, most of which are white, and which are anatomically 

 as distinct from the heliconidfe as a lion from a bufl'alo. 

 But of these pieridae there is one genus, the leptalis, which 

 exactly resembles the heliconias in external appearance. So 

 close is the resemblance that such expert naturalists as Mr. 

 Bates and Mr. Wallace have been repeatedly deceived by it 

 at the time of capture. Moreover, each species of this genus 

 leptalis is a copy of the particular species of heliconia 

 which lives in the same district. Every band and spot and 

 fleck of colour in the heliconia is accurately reproduced in 

 the leptalis ; and besides this, the lazy mode of flight is also 

 imitated. While in point of numbers, we find about one 

 leptalis to a thousand heliconias. ISTor is this the only 

 instance. So pre-eminently favoured are these beautiful 



