( cxxvi ) 



by way of distinction, may be designated as discriminate poly- 

 morphism, when, for example, a species exists in widely different 

 surroundings, and its different vai-ieties are allocated, and, if 

 one may say so, attuned, to fitting localities or, it may be, 

 seasons, as in the case of some local or seasonal variety, or the 

 many species which rest by day on objects of varied aspect, 

 the colours or markings of which resemble their own, and 

 often in attitudes adapted to increase the illusion.* 



Indiscriminate polymorjjhism. 



There is another class of cases to which I do not know that 

 a better name can be applied than that of indiscriminate poly- 

 morphism, consisting of such as do not fit their variations to 

 appropriate localities, seasons, resting places or resting attitudes. 

 To these polymorphism may be advantageous on the principle 

 that as every different colour or marking has its own special 

 chance of escape from enemies, the more colours or markings its 

 different individiials present the more chances of escape they 

 would have ; just as if one could conceive a billiard table to be 

 fitted up with many holes of different shapes and a number of 

 balls of different shapes to be scattered over it, more balls 

 would find places than if all the balls were of one size. 



Characters " biologically indifferent." 



But I do not think these explanations can be considered 

 to cover the whole ground. The only explanation that seems 

 to me possible in the vast majority of cases is that many 

 characters, even striking ones, are, as previously stated, "biologi- 

 cally indiffei-ent." f Nature, it may be said, is more tolerant 

 than is sometimes supposed, when, for example, it is said 

 that the slightest diff'erence in conspicuousness must tend 



* Such as Hihcrnia leucopheearia resting on oak trunks. — Proc. Ent. 

 Soc. Lond. 1903, p. ix. This resting situation and position is one of the 

 points on which more observation is wanted. Some moths strongly variahle 

 in appearance ai'e notorious for not resting on surfaces suitable for con- 

 cea\ment,a,s Polia chi. — Barrett's " British Lepidoptera," vol. iv, p. 307. Can 

 these be shown to be nauseous or in some otlier way exempt from attack ? 

 As bearing on this, see Mr. Porritt's paper before referred to. 



t "Weismann is of opiiuon that where species are variable in a high 

 degree their variations possess no biological importance, or the less valuable 

 among them would be gradually removed by selection. — "Evolution 

 Theoryj" vol ii, p. 135. 



