28 



KNOWLEDGE 



[Febbdary, 1902. 



hoppers. To such a degree has the imitation been 

 carried in Ccroxylus that the insect looks ex.aetly like a 

 twig overgrown with moss. By reason of its resemblance 



Fig. 1. — Mimicrv in Butterflies. 1. Leptalia Type, 

 mimicking. 3. Itliomia, model. 



2. Lcptalis 



to a bee the fly Valucella can enter the hive and leave 

 its eggs without exciting the suspicions of the bees. 

 Certain clear-winged moths are also liable to be mis- 

 taken for bees and hornets. 



Protective colouring is very common in the plumage 

 of birds, a green woodpecker, for instance, is not easily 

 distinguished amid the surrounding moss and foliage. 

 Cuckoos are often mistaken for hawks, which they much 

 resemble both in appearance and flight. Dun-coloured, 

 tawny, striped and spotted animals are difficult to 

 detect amid their nativj haunts. The fur of a number 

 like the ai'ctic hare and fox becomes white in winter, 

 harmonizing with the snow-covered gi'ound. Most of 

 the autumnal Lepidoptera are brown or golden, while 

 the winter species usually assume a grey or silvery garb. 

 Snails and caterpillars are familiar instances of pro- 

 tective colouring, but this mode of concealment is so 

 general throughout the animal kingdom that it is 

 unnecessai'y to multiply examples. 



Animal Homomorphism is illustrated by the Polyzoa, 

 which outwardly resemble the Hydroid Polypes and 

 corals, though they belong to a different sub-kingdom. 

 Amphibians like Caecilin assume a worm-like aspect, 

 and armoured creatures such as the tortoise, armadillo, 

 ganoid fishes and crustaceans present analogous forms. 

 Many of the smaller crustaceans take on a resemblance 

 to various families of insects ; some butterflies and 

 moths in general appearance come vei-y near the 

 humming birds. The porcupine is a rodent, the hedge- 

 hog one of the Insectivora, their relationship is not so 

 close as one might imagine from their exteraal 

 appearance. Among the Marsupials of Australia forms 

 occur closely con-esponding to members of other ordei-s 

 inhabiting other regions. The resemblances of the 

 shrew to the common mouse, of the bat to a bird, and 

 of the whale and dolphin to a fish are examples of 

 homomorphism which will occur to every reader. 



Similar habits, if these may be included under 

 homomoi-phism, are sometihies possessed by animals not 

 closely related. The exceptional habit of the cuckoo is 

 shared by several North American birds belonging to a 

 widely different family. Mr. Darwin mentions species 



of Molthrux allied to the starlings which resemble the 

 cuckoo in building no nest of their own and in laying 

 their eggs in the nests of other birds. A similar habit 

 appears in the cuckoo-bees. There is also the case of the 

 cuckoo-flies, which live as inciuilines in the galls of other 

 insects. The ventriloquism or intentional imitation of 

 the mocking bird also might almost be viewed as a case 

 of homomorphism. 



The vital phenomena of plants and animals are so 

 near akin that it would be strange if we did not meet 

 with con-esponding facts in the vegetable kingdom. 

 Mimicry is perhaps more frequent in the seed than in 

 any other part of the vegetable organism ; it occurs, 

 however, in other organs, and even the entire plant body 

 may assume a deceptive appearance. A well-known 

 example is the white dead nettle, which so closely 

 resembles the stinging nettle in size and in the shape 

 and arrangement of its leaves. In systematic position 

 the two plants are widely removed from each other, but 

 thev gi'ow in similar situations and are easily mistaken; 

 anyone who has occasion to collect quantities of Lamium 

 is almost sure to get his hands stung by Urtica, an 

 experience calculated to convince one of the efficacy of 

 protective resemblance. Among animals it is species 

 provided with formidable weapons of defence that are 

 most frequently mimicked by weak defenceless creatures. 



Fia. 2. — Urtiea and L; 



The stinging nettle is therefore a very likely model for 

 unprotected plants to copy. 



A somewhat analogous case is the yellow bugle of 

 the Riviera, which has its leaves crowded and divided 

 into three linear lobes, some of which are again divided. 

 In this the plant differs very greatly from its allies ; it 

 has, however, acquired a very striking resemblance to a 

 species of Etiphtjrbiti, abundant on the Riviera. The 

 acrid juice of the Euphorbias secures them immunity 

 against a host of enemies. As the two plants gi-ow 

 together there is little room to doubt that, like the dead 

 nettle, the bugle profits by its likeness to its well pro- 

 tected neighbour. 



The rare heath Menziesia cneruJea. thought to be pro- 

 tected by its marked resemblance to the CrowbeiTy 

 [Empetrum nigrum), has also been adduced as a probable 

 case of mimicry. 



