1908.] IN THE MUSTELINE CARNIVORA. 945 



from the usual rule"* ; and Mr. Lydekk'er observes : " It is also 

 noteworthy that in the parti-colom-ed examples [of the Mustelidse] 

 there is a great tendeiicy for the underparts of the body to be 

 darker tlian the upper ; whereas, it is scarcely necessary to 

 observe, the reverse is the case in the great majority of 

 mammals." t 



Befoi^e the publication of Mr. Thayer's paper explaining the 

 celative or procr3^ptic significance of the usual style of coloration 

 whereby reflected lights are toned down and shadows obliterated^ 

 it was hardly to be expected that any special inquiry would be 

 made as to the meaning of the peculiar livery of the Mustelines 

 in question ; but, so far as I am aware, no suggestion has been 

 made on this head since the publication of that luminous idea J. 

 Yet the inference seems obvious enough that, since the colours 

 are reversed, their functions must also be reversed ; that is to 

 say, if animals which are light below and dark above are concealed 

 on this account under a top light in their normal suiToundings^ 

 those which are light above and dark below should be made con- 

 spicuous under the same conditions. White on the upper side 

 should have the efiect of enhancing reflected light, and dark on 

 the under side the effect of emphasising shadows, 



A simple experiment demonstrates this to be a fact. If a cork 

 be pinned with a long pin against a sheet of brown paper of its 

 own colour under a top light, it may be made practically invisible, 

 as Thayer has shown, by painting its upper side dark and its 

 under side white. But if the cork be then turned over so that 

 its white side be uppermost and its dark side undermost, its 

 maximum of conspicuousness is achieved. The effect of turning 

 it over is much the same as that produced by immensely increas- 

 ing the intensity of the top light over the uncoloured cork. 



In the case of Mammalia, it is exceptional for the coloration to 

 be of a kind that makes for conspicuousness. In the majoiity of 

 instances it is procryptic for the purpose of enabling the indi- 

 vidual either to escape enemies or to secure prey. Hence, if it 

 be claimed that the livery of these Mustelines belongs, as I think, 

 to the former category, it is necessary to produce in favour of the 

 claim evidence drawn from the bionomics of the species in addi- 

 tion to that deducible from the above mentioned fact that the 

 coloration is the very opposite of that exhibited by a very large 

 number of procryptically coloured forms. Suflicient evidence to 

 justify the adoption of this view as a useful working hypothesis, 

 is, in my opinion, supplied by what is known of the habits of the 

 species discussed in the following pages. 



With the exception of mimetic species, animals which are 

 coloured so as to be conspicuous in their natural surroundings 

 are very often px-otected from enemies by distastefulness arising 

 from a nauseating flavour or odour, or by the possession of poison- 



* J. G. Wood, ' Illustrated Nat. History,' Mammalia, p. 372, 1861. 

 t Rnyal Natural History, ii. p. 47, 1894. 

 t ' The Auk,' xiii. 1896, pp. 124 & 318. 



60* 



