3 66 



SCIENTIFIC NEWS. 



[Oct. 5, ii 



animals have less decided and less manifold colours 

 than those which lead an independent existence. 



Aquatic animals have in general more uniform and 

 less intense colours than terrestrial forms. Pelagic 

 species have rare and strikingly deep colours — a fact 

 perhaps connected with the frequent transparency of 

 their bodies. 



Sea-animals which live among algae and generally in 

 situations rich in marine vegetation, have a more varied 

 and lively range of colouration than such as live among 

 stones or on a sandy or muddy bottom. 



The dull, sombre colour of fresh-water insects is too 

 well known to need more than a passing notice. Some 

 species, however, which pass their larval state in water, 

 e.g., dragon-flies, display a brilliant colouration when 

 mature. 



Land animals which live in the woods, beneath herbs, 

 on bushes or on flowers, etc., have more varied and 

 striking colours than the inmates of sandy or rocky 

 localities. The "Desert colour" of the Arabian and 

 Saharan fauna, the former more especially, has been 

 particularly dwelt on by Canon Tristram. 



Contrary to the somewhat premature assertion of Mr. 

 Grant Allen, there is no universal and constant connec- 

 tion between the colouration of animals and the nature 

 of their diet. Insectivorous, or rather zoophagous 

 animals which live under leaves or among flowers, are 

 often brilliant and varied in hue, whilst plant-eating 

 species, if they do not regularly inhabit leaves and blos- 

 soms, are often dull and sombre in colour. 



Still this generalisation is as far as that of Mr. Grant 

 Allen from accounting for the gorgeous colouration of, 

 e.g., the genus Phamus, devourers of carrion and excre- 

 ment among which they make their abode. 



The richer an animal group is in species the more 

 varied, and in many cases the brighter is their colouring 

 — a rule well exemplified in the humming-birds. But 

 it fails us in not a few striking cases, among which we 

 need merely mention the great group of the Brachelytra 

 or rove-beetles, the Harpalidce, and the genus Aphodius. 



The development of colour bears no direct proportion 

 to the quantity of light to which the animal is exposed. 

 It is rather directly connected with the general develop- 

 ment of the animal. Deficient nutrition and diseases 

 impoverish the colours. 



Large animals have, for the most part, a duller colour 

 than smaller species. We need scarcely add that the 

 views ofSignor Camerano as regards the influence of light 

 agree substantially with those of Mr. A. R. Wallace. 



A very dry climate seems to darken colours, whilst a 

 very moist one brightens or lightens them. The colours 

 of animals are modified by the altitude of their station 

 above the sea-level. The higher we rise, thinks Signor 

 Camerano, the more intense are the colours which en- 

 counter our view. 



With this proposition we cannot agree. A mountain 

 fauna is generally more sombre than that of the adjacent 

 plains — a remarkable contrast to the Alpine flora. This 

 fact, indeed, has been cited as an argument against Mr. 

 Grant Allen's theory of the colouration of animals. 



Species confined to islands have often darker colours 

 than those inhabiting continents. This conclusion holds 

 strikingly good as regards many varieties inhabiting small 

 islands. 



It will be seen that the colouration of any given fauna 

 is a result depending on a complex of factors, the re- 

 spective influence of which it is hard to estimate. 



The different zoo-geographical regions of the earth 

 seem to have certain more or less predominating colours. 



In the Palasarctic region, white, grey, black, and 

 yellowish are frequent ; in the Ethiopean, yellow and 

 brown ; in the Neotropical, green and red predominate (?); 

 in the Indian the yellow tones occur very plentifully; 

 whilst in the Australian dark colours, and especially 

 black, take the lead. 



In almost all groups of animals those parts which are 

 less visible are often brightly coloured or spotted, whilst 

 the other parts of the body are more frequently uni- 

 coloured, or dark. Here, however, we are reminded of 

 the very numerous cases in insects where the brightest 

 colours appear to be seated in projecting parts, such as 

 the extremity of the abdomen, the tips of the elytra in 

 Coleoptera and Hemiptera, the margins of the wings in 

 butterflies, etc. So frequent is this phenomenon that 

 some naturalists have regarded it as a protective arrange- 

 ment — a bird, e.g., being more likely to strike at these 

 bright, outlying parts than at the more sombre vital 

 regions. 



In many cases the young of different species re- 

 semble each other closely in colouration, though the 

 adults are quite distinct. 



While thus giving an abstract of the very interesting 

 results of Signor Lorenzo Camerano, we are fully aware 

 that some of them require further consideration. It must 

 have struck many of our readers that inquiries on the 

 colouration of animals have, so far, left the physical side 

 of the question scarcely touched. The production of the 

 colouring-matters, their occurrence in one species and 

 not in another, and the mechanism of their distribution 

 have still to be dealt with. It strikes us that in the pro- 

 duction of the design — in e.g., the wings of a butterfly — 

 the principles of capillary attraction and of diffusion must 

 come into play. By mixing certain colours which have 

 different rates of diffusion and placing a small drop of 

 the mixture on white blotting-paper, designs may some- 

 times be obtained which roughly resemble those we meet 

 with in the wings of Lepidoptera. 



THE ELECTRICAL TRANSMISSION OF 

 POWER. 



A Lecture Delivered by Professor Ayrton, F.R.S., etc., 



BEFORE THE BRITISH ASSOCIATION, ON SEPTEMBER 8tH, f 

 AND RE-DELIVERED TO THE WORKING-CLASSES OF \ 



Bath, on September 13TH, 1888. 

 (Continued from p. 321.^ 



LET us study this electric transmission a little in 

 detail. I pull this handle, and the bell at the other 

 end of the room rings, but in this case there is no visible 

 motion of anything between the handle and the bell. 

 (Electric bell rung by an electric current produced by 

 pulling the handle of a small magnetic-electric machine.) 

 Whether I ring the bell by pulling a wire, or by sending 

 an air puff, or by generating an electric current by the 

 exertion of my hand, the work necessary for ringing the 

 bell is done by my hand exactly as if I took up a hand 

 bell and rang it. In each of the three cases I put in the 

 power at one end of the arrangement, and it produces its 

 effect at the other. In the electric transmission how 

 does this power travel ? Well, we do not know : it may 

 go through the wires, or through the space outside them. 

 But although we are really quite in the dark as to the 



