214 



HARDWICKE'S SCIENCE-GOSSIP. 



[Nov. 1, 1S6S. 



said that the species were created so ; but, if this 

 were the case, why should some Corsican species 

 have beeu created like those of the mainland, while 

 others differ more or less, so as to be reputed as 

 well-marked local varieties, or even perfectly dis- 

 tinct species ? If for the mere sake of variety, why 

 should not all the species vary, and why should not 

 every few miles of country have its distinct varieties 

 or species instead of the most distinct forms of the 

 whole Continent showing themselves on two small 

 detached islands alone ? 



The occurrence of arctic species on the moun- 

 tains of warmer climates is explained by Mr. 

 Darwin to arise from the equatorial migration of 

 all organisms at glacial periods (for it is the 

 opinion of some eminent naturalists that there is a 

 regular recurrence of glacial and tropical periods), 

 when the arctic species were driven south and north 

 to the plains of temperate climates, and the tem- 

 perate species to the tropics. When the cold 

 decreased, the arctic species would retreat towards 

 the poles, and would ascend the mountains, where 

 a few still remain. Some of the temperate species, 

 at the same period, appear to have penetrated to the 

 equator, with or without the aid of mountains ; and 

 on the return of the warmth were driven both north 

 and south, which will account for the presence of so 

 many identical temperate species both north and 

 south of the equator. 



One of the most singular phenomena which can be 

 philosophically explained by Darwinism is that of 

 mimicry,* i.e. the assumption by helpless animals of 

 the colours or markings of those which are better 

 protected, or else of inanimate objects. Thus the 

 colour of desert animals is usually sandy. The 

 common frog, which lives in muddy water, is mud- 

 coloured, while the tree-frog is green. Arctic 

 animals are almost invariably white. But, leaving 

 these general resemblances, let us come to what is 

 called mimicry proper, the assimilation of one 

 animal to another totally unconnected with it. The 

 most striking instances of this occur among insects. 

 Insects will imitate flowers, leaves, snakes, and 

 almost every conceivable object, but most frequently 

 other insects'which are better protected. A cater- 

 pillar, supposed to be that of one of the Bomhycidm, 

 or silkworm moths, was once observed by Mr. Bates 

 in South America, which presented such an extra- 

 ordinary resemblance to a small venomous snake as 

 to frighten all the natives to whom he showed it. 

 The bee-hawkmoths, and the clear-wing hawkmoths 

 generally, present so striking a resemblance to bees, 

 wasps, hornets, and other stinging insects, as at 

 times to deceive the entomologist. There is one 

 large family of butterflies, the Heliconidce (also in- 



* Compare the able article on " Mimicry and other Pro- 

 tective Resemblances among Animals," in the Westminster 

 Review for July, 186r. 



eluding the old families, Banaidm and Acrceidce) 

 all whose members exude, when touched, a disagree 

 able, ill-smelling fluid, which appears to render them 

 obnoxious to birds and other insectivorous animals. 

 One group is almost peculiar to Africa, another to 

 the East Indies, and another to South America ; 

 and in all these countries we find butterflies belong- 

 ing to several other groups, and even moths, which 

 resemble them so completely that they are at times 

 undistinguishable from them without close exa- 

 mination, and when on the wing must be per- 

 fectly so. All these mimicking species are much 

 rarer than the insects they mimic, and are evidently 

 mistaken by birds for uneatable insects. It there- 

 fore appears that as the insects of waning groups 

 decreased iu numbers, a sligh't variation, tending to 

 assimilate them to those of a dominant group, would 

 be beneficial to them, while the individuals which 

 did not present it would be inevitably destroyed ; and 

 the ultimate effect of this would be that the variety 

 would more and more assimilate itself by natural 

 selection to the common species, till it became in 

 time, perhaps, almost identical in appearance with 

 it, and would thus be preserved when no other 

 safeguard would avail it. The preservation of the 

 female is of far more importance in many animals 

 than that of the male, and so we often find the 

 female protected by mimicry, dull colours, and 

 similar means, while the male has no such pro- 

 tection. 



We have now bestowed a passing glance on a few 

 of the most remarkable of Mr. Darwin's theories 

 and arguments, as laid down in his celebrated book 

 " On the Origin of Species," and have also briefly 

 noticed one or two of the more interesting subjects 

 which have been discussed by his followers since 

 its publication ; but to go fully into a subject, each 

 of whose branches would require at least an entire 

 volume for its elucidation, is of course impossible 

 here. But whether we go to the extreme length 

 of the theory, and believe with Mr. Darwin that 

 all the forms of organic life have originated from 

 half a dozen primordial germs at most— and probably 

 from one only — or whether we are simply led from 

 an examination of his arguments to the conclusion 

 that species are more variable than is commonly 

 supposed, it is scarcely to be disputed that the 

 whole subject is worthy of far more serious attention 

 from the general public than it has hitherto 

 received ; and if these few pages shall have the 

 effect of calling the attention of one unprejudiced 

 thinker to the subject, our object will have been 

 attained. 

 Dublin. W. E. Kirby. 



Eleas.— During the drought we rarely ever saw 

 such a thing as a flea ; but the rain had scarcely 

 visited us before we were infested, so much so as to 

 become a task to rid ourselves of them.— 6?. Bidlard. 



