294 



KNOWLEDGE & SCIENTIFIC NEWS. 



[December, 1905. 



will be visible externally in the animal's coat or 

 plumage. 



Before going further it would be well to define 

 exactly what I mean by vigour. 



I prefer to employ a term which ha.s already been 

 used in a somewhat similar sense by Wallace and other 

 naturalists, rather than coin a new one* 



By vigour is meant wh;it one would popularly describe 

 as " high fettle " or " condition." .\n athlete trained 

 for a race is full of " vigour " so far as his mu.scles are 

 concerned. 



Physiologically speaking, however, I mean by " high 

 vigour " thai an animal's whole bixly is in that state 

 of physiological activity which would enable it to stand 

 severe strains and exertions without being adversely 

 affected. 



" .Activity of nutrition and function " (the phrase is 

 borrowed from Dr. \. E. Durham, in Quain's Medical 

 Dictionary) is the best definition of what I mean by 

 " vigour." 



So that :— 



The colour of an animal will be primarily dependent 

 on its " activity of nutrition and function " being at 

 a high or low level. 



.An animal's " vigour " is affected by several causes. 



I St. CLIMATE. -A heading which may be again 

 sub-divided into 



((?) Temperature. 

 (b.) Food supply. 



2nd. The rise and fall nf se.xual activity. 



In those animals whose vigour is not constant 

 throughout the year, the changes will take place in 

 rorrelrition with one or other of these causes. 



The effects of the first we may call seasonal change in 

 contradistinction to the second or breeding change. 



I now propo.se to consider the mammals and birds 

 according to the regions (Polar, Tropical, or Temper- 

 ate), in which they live. 



1. — The Polar Regions. 



In the Polar regions the period of extreme cold and 

 scarcity of food is so long as compared with the short, 

 bright summer, and the transition from the one to the 

 other sfi abrupt that the inhabitants thereof will be 

 subject to violent changes. 



The winter follows so quickly after the breeding 

 season that there is no lime, as in more temperate 

 regions, for the animal to recuperate after the lowering 

 effects of sexual activity. .Such reserve material as is 

 formed will, therefore, be stored up in the ff)rm of fat, 

 a condition in which it is most accessible for any siib- 

 setiuerit demands that may be made upon it by the body. 

 Tliis storing up of fat, as Captain Barrett-Hamil- 

 ton has shownt, is f)ne of the concomitants of sluggish 

 metabolism. Here, therefore, we have conditions of 

 low vigour, and in cf)rrelation with them we find the 

 .inimals for the most part white or grey. 



In the spring we would expect that the excitability 

 of the breeding seasf>n, as well as the higher tempera- 

 ture and more plentiful food, would fend to a high state 

 of vigour, but it must b<: remembered that the privji- 

 tions of the winter h.ive so lowered the animal's condi- 

 tion, that it is unable to derive full advantage from the 

 more favourable circumstances, and its vigour is, 

 therefore, unable to reach a high level. In correlation 



with this we find a predominance of duller colours 

 amongst the majority of Polar animals. 



How, then, are we to account for the darker animals 

 of these regions, as, for instance, the musk ox. pen- 

 guins, and raven? 



If our suggestion holds good, the fact of these 

 animals being dark coloured in the.se regions proves 

 that they are able to maintain their full vigour through- 

 out the year, in spite of the cold and scarcity of food.* 

 \ow if this be so, we ought to find these animals 

 throughout the world equally highly coloured or more 

 so, or it is conceivable that if their " vigour " is so 

 great in cold localities, it might liecome too great in 

 warmer regions, and being unable to find any outlet for 

 this excess (the animal being already highly coloured), 

 death might ensuet, and such nniinais would, in con- 

 sequence, be restricted to the colder portions of the 

 world. The raven is a good example of the first of 

 these conditions, for the Corvida; exist practically un- 

 ch.inged throughout the world, and the musk ox and 

 lemming fulfil the second. The mouse hares (Ocla'tona), 

 although .Alpine rather than Arctic, give us a good idea 

 of seasonal change, and show us that the amount of 

 " \igour," rather than the climate, may affect their 

 colour. 



For example, tivo species — O. ladacensis and O. 

 roylei — inhabit adjacent countries where climatic condi- 

 tions are very similar. Ladacensis is white, or nearly 

 so in winter, and light brown in summer, whereas 

 rnylci, which becomes bright red in summer, never be- 

 comes paler than iron grey in winter. 



So that here we have two nearly-allied species in- 

 habiting the same country, each equiilly influenced by 

 the climate so as to cause them to undergo a seasonal 

 change, yet in winter one is white and the other — in 

 defiance of the laws of protection — dark. Captain 

 Barrett-Hamilton has also brought to my notice another 

 similar instance in the ca.sc of the .Siberian lemmings 

 (Dichrnstonyx and Lemniis), where the light or pro- 

 tectivelv-coloured species is much scarcer than its more 

 conspicuous relative. 



The penguins, again, are birds whose nature is such 

 as to enable their " vigour " to reach its fullest extent 

 in .\ntarctic regions at all times of the year. It is not 

 surprising, therefore, to find several specimens, e.g., 

 the emperor penguin, indulging in p.'ilches of bright 

 colours, such as yellow, orange, or red, thus affordins; 

 a further proof that " vigour " rather than " cjiniale " 

 is the prime factor in determining the color.ilion. 



To carry our point further, we should expect to liiid 

 the vigorous, dark .Arctic species breeding e;uli<'r than 

 those that are paler coloured, .and in confirmation of 

 this we find the raven breeding very <"arly in .April, 

 while the ptarmigan antl grouse wait till the l:itter end 

 of .May. 



The lemming is .another inst;mce, for it is .1 liriglitlv- 

 coloured animal, and in certain seasons produces young 

 more numerously and rapidly than .any other Arctic 

 animal, while as a result of this excessive " vigour," 

 we find it most pugnacious and energetic. 

 (To be continued. ) 



•The following writers may be said to have written on the subject 

 from this standpoint, viz , Bateson. Barrett-Hamilton, Beddard. 

 Cnnningham, Geddes and Thompson, Newbigin, Tylor and 

 Wallace. 



^Proc. Roy Irish Arad. Vol 24, Sect, B, Pi. 4, P 307(1903) 



• It might be argued against this that in these cases, the colour 

 having been placed in the hair, it could not be withdrawn, and not 

 being harmful, but even, perhaps, useful (ashaslicen suggested for 

 the musk ox), the animal was enabled to survive. If these animals 

 only moulted in spring, such an argument might hold good ; but in 

 the case of the raven, the moult is in autumn, and I fancy the 

 same holds good for the penguins. 



t The excessive cncigy of white men on first coming to the 

 tropics is a frequent cause of their overtaxing their powers, so 

 frequently culminating in drink or fever. 



