HARDWICKE'S SCIENCE-GOSSIP. 



217 



THE COLOURS OF ANIMALS. 5 



* 



naturalist. 



J^j^fS^ HE beautiful and 

 varied colours ex- 

 hibited by animals 

 and plants have 

 from the earliest 

 times excited the 

 admiration, and 

 stimulated the curi- 

 osity of mankind. 

 Whether they have 

 been explained as 

 destined chiefly to 

 please the human 

 eye, or as of some 

 use in the economy 

 of the organism 

 possessing them, 

 they have been a 

 never-failing source 

 of interest to the 

 The more or less general acceptance of 

 Mr. Darwin's views on the origin of species led to a 

 revolution in our method of regarding organic nature ; 

 and the problem, how the various wonderful colours 

 of plants and animals are to be explained, from the 

 point of view of natural selection, has ever since been 

 one of the most fascinating of the many interesting 

 problems before the biologist. A great deal of work 

 has already been done in this field, and the colours of 

 flowers, the very brilliant (not to say glaring) colours 

 of many insects, as well as the more sombre hues of 

 many animals of all classes have in turn been 

 explained on Darwinian principles : while Mr. 

 Darwin himself in his famous theory of sexual 

 selection has attempted to account for the brilliant, 

 varied, and most beautiful colours so often connected 

 with the period of courtship. 



In Mr. Poulton's recently published work on this 

 subject, the author has given us an extremely 

 able and interesting summary of our present know- 

 ledge of the colours of animals. His frank and 

 sturdy Darwinism makes his book a great contrast to 



■ * "The Colours of Animals, their Meaning and Use: espe- 

 cially considered in the case of Insects." By E. B. Poulton, 

 F.R.S. (Inter. Scient. Series). 



No. 310.— October 1890. 



one or two recent volumes in the same series. His 

 position is best shown in his own words : " I fully 

 believe that further knowledge will prove that this 

 principle (natural selection) explains the origin of all 

 appearances, except those which are due to the 

 subordinate principle of sexual selection, and a few 

 comparatively unimportant instances which are due 

 to isolation or to correlation of growth." * From this 

 point of view no better man of science could have 

 been found to write the present volume. Mr. 

 Poulton is an able biologist, an enthusiastic naturalist, 

 and one of the leaders of the Neo-Darwinian School 

 in England ; while it is superfluous to remind 

 any one interested in the subject of his own im- 

 portant experiments on the colours of insects, 

 especially on the variable protective colouration of 

 lepidopterous larvre and pupse. 



The book opens with a clear account of the 

 physical cause of animal colours, which is summed 

 up in the following words : " All these causes of 

 animal colours may be conveniently grouped under 

 two heads ; (1) pigmentary, and (2) structural. The 

 first head includes colours caused by absorption, and 

 the effects produced vary with the chemical nature of 

 the substance (pigment). The second head includes 

 the colours or appearances produced in all other 

 ways, the efficient cause being the structure of the 

 substance rather than its chemical nature." t 



After pointing out that all colours must have been 

 originally non-significant, thus forming the material 

 out of which various selective agencies have produced 

 the colours with a meaning, and citing cases of non- 

 significant colour, Mr. Poulton goes on to discuss 

 cases in which colour may be of direct physiological 

 value to the organism, that is, take part in some vital 

 function. This must be distinguished from what is 

 now usually called the "biological " value of colour, 

 which gives the organism some advantage in its 

 relations with other species. The green colour of 

 chlorophyll is a well-known instance of the former ; 

 but "no equally clear instance has been proved to 

 occur in the animal kingdom." Mr. Poulton, how- 

 ever, discusses Lord Walsingham's interesting 



* Preface, page viii. 



f Page 11. 



