July 1, 1892.] 



KNOWLEDGE 



121 



^^ AN ILLUSTRATED "^^ 



MAGAZINE OF SCIENCE i 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: JULY 1, 1892. 



CONTENTS. 



PAGE 



Protective Resemblance in Animals. By R. Ltdekkee, 



B. A. Cantab 121 



Some Practical Applications of Electricity. Bv J. J. 



Stewabt ... ... .. ... ... ... ... 124 



Bee Parasites— I. By E. A. Butleb 126 



The Distribution of Sunspots in Solar Latitude. Bv 



E. W. Matindee, F.R.A.S. 128 



What is a Nebula? By A. C. Kaxtaep 131 



Letters :—W. H. S. MoxcK ; A. C. Raxtaed ... 132,133 



The Fesdin* of a Plant. By J. PEyiLAXD Smith, M.A., 



B.Se. 134 



Some Facts about Explosives. By VACGHAy Coexish, 



B.Sc, F.C.S 136 



Radlometry. By A. Jamesox 138 



Chess Column. By C. D. Locook, B.A.Oxon 139 



PROTECTIVE RESEMBLANCE IN ANIMALS. 



By R. Lydekker, B.A.Cantab. 



THAT the colours of animals tend to assimilate 

 themselves to the natural surroundings of the 

 animals themselves is a fact which has been long 

 known in natural history ; and it is, indeed, one 

 which is self-apparent to every .sportsman and to 

 every traveller in the wUder regions 'of the globe. For 

 instance, everyone is probably aware that desert-hauntmg 

 animals, like lions, gazelles, wild asses, jerboas, and 

 many species of birds, generally have a uniform sandv- 

 coloured coat, which renders them at a short distance 

 almost or completely in%-isible in their native wastes. 

 Then, again, every Enghsh sportsman knows how com- 

 pletely the coloration of the partridge and the hare assimi- 

 lates with that of the stubble or ploughed fields in which 

 they are wont to lie ; while the mottled blacks and browns 

 of the woodcock and snipe accord so exactly with the hues 

 of decaying leaves and grass that the inexperienced eye 

 will often faU to detect a wounded bird even when Iving 

 dose to the feet, and scarcely anyone can distmgiiisb 

 the living birds when on the ground. The brilliant 

 vertical orange and black stripes of the tiger and zebra, 

 when seen m a menagerie or a museum, do not strike us as 

 resembhng anything in inanimate nature. In its native 

 jungle, largely composed of upright yellow stems of tall 



grasses, between which are narrow intervals of deep black 

 shade, the colour of the tiger is, however, admirably 

 suited to its sm-roundings : and it is stated that the stripes 

 of the zebra are arranged in such proportions as exactly to 

 match the pale hue of arid ground by moonlight, so that 

 on such occasions these animals are absolutely invisible 

 even at very short distances. We hardly need refer to the 

 white colom- of polar animals, such as bears, ermines, 

 foxes, hares, &c., as the most perfect example of this kind 

 of protective coloration ; and numerous other examples 

 will at once present themselves to the reader. 



\\ eU known as are these comparatively simple instances 

 of protective resemblances, there are, however, others of 

 a more striking nature, where the animal either resembles 

 the form of some inanimate object, or that of some other 

 kind of animal which has especial means of protection ; 

 and since these resemblances are less generally known, 

 they will form the subject of the present article. The 

 term " protective resemblance " is generally applied to those 

 instances where the animal resembles more or less closely 

 an inanimate object, and thus renders itself inconspicuous ; 

 while the instances where one animal assumes the appear- 

 ance of another, and thereby becomes conspicuous, are 

 classed under the term •' mimicry." It wUl, however, be 

 obvious that both these kinds of resemblances are near 

 akin, and are far in advance of protective coloration, pure 

 and simple, where no imitation of form takes place. We 

 shall first mention some instances of the imitation of the 

 forms of inanimate objects by animals, and then refer 

 to those cases where other animals are the objects of 

 imitation. 



Some of the best examples of what we shall take leave 

 to call inanimate mimicry are to be found among insects, 

 and we shall take our first case from among the butter- 

 flies. AU are probably aware that a large number of these 

 insects, such as our common peacock and tortoisesheU 

 butterflies, while brilliantly coloured on the upper surfaces 

 of their wings, have the under surfaces of the wings of a 

 dull, sombre hue ; and most of us have doubtless been 

 almost startled at the suddenness with which one of these 

 gaudy creatm-es seems to vanish altogether when it settles 

 on dark ground or the rough bark of a tree, and at once 

 closes its wings. Here, then, we have an instance of 

 ordinary protective coloration, without any attempts of 

 mimicry of fonn. There is, however, a peculiar group of 

 butterflies allied to om- own pm-ple emperor, inhabiting 

 Northern India and the Malayan region, which have gone 

 far beyond this simple kind of protective resemblance, 

 and actually imitate the form of leaves growing on their 

 native branches. These butterflies ( scientifically known 

 as CalliiiKi), one of which is figured in the accompanying 

 cut, have the upper surface of the wings briUiantly 

 marked with orange, their 6-ont wings terminating in a 

 sharp point externally, and the hind ones in a "tail," 

 after the fashion of our swallow-tailed butterflies. Between 

 the sharp point of the front and the tail of the hind -n-ing 

 there runs on the under surface a curved line, from which 

 srnaller lines are given off to the edges of the wings. 

 When this butterfly settles on the stem of a plant bearing 

 pointed leaves and closes its wings, the points and tails of 

 the same of course come into exact opposition ; and since 

 the tail of the wings is closely applied to the stem of the 

 plant it appears exactly as though it were the stalk of a 

 leaf, the midrib and veins of which are exactly imitated 

 by the lines on the under surface of the wings ; "while the 

 apex of the leaf is formed by the opposed points of the 

 front wings. So exact is the resemblance of the butterfly 

 when in this position to a faded leaf, that, as Mr. Wallace 

 tells us, it deceives the eye even when gazing full upon it ; 



