4o6 NATURAL SCIENCE. Dec . 1895. 



Viewing together the three varieties mentioned, it looks as if they 

 had diverged from, and multipHed at the expense of, an older stock, 

 by virtue of something inherent in the additional outlay of colouring 

 matter, the precise shade of which seems to be immaterial. 



I think that the two facts of the severe struggle for existence 

 and of the predominance which races like nigyiventrls have been able 

 to assert over less pigmented forms afford demonstrative evidence 

 that abundant pigmentation, the expression of intense metabolism,' 

 must be associated with superior physical vigour. That is, that the 

 most ornamental varieties {ceteris paribus) necessarily must — not 

 generally do — increase. If the survival of the physically fittest 

 has coincided, as is here the case, with that of the most intensely 

 coloured, the indifferent characters of this species cannot bs regarded 

 as mere awkward bye-products of growth : their formation seems to 

 have been conditional, rather than incidental, to continued existence. 



It appears from this that "useless characters" and "characters 

 of no active utilitarian significance " are not interconvertible terms. 

 And unless this conclusion is applicable only in the matter of the 

 production of superabundant colour, and only to the case of L. muralis, 

 I think its bearings are not easily appreciated. 



Speaking apart from structures and anything else that may 

 possess a life-preserving value, it may be said that an unbroken 

 gradation exists from the most decorative ornamentsof higher animals, 

 peculiar to one sex, to the wider class that contains the ordinary non- 

 ornamental useless characters of higher and lower animals of both 

 sexes. And it has been remarked with surprise that representative 

 or allied species of animals and plants often differ from each other in 

 respect of such non-utilitarian (morphological) characters, whence the 

 awkward question has arisen how they ever came to be differentiated, 

 seeing that it mattered nothing to their ancestors, as varieties 

 deviating from another type, whether they possessed this or that non- 

 adaptive feature. Why should they have survived while others 

 perished ? 



The sphere of utility would be extended if, reviewing them as we 

 now do the dominant sub-species of L. muralis, we could demonstrate 

 that their ascendency over innumerable, afterwards extinct, connect- 

 ing forms had been determined by a physical superiority, to which 

 the " useless" character, whatever it ba, still bears testimony. 



G. NoRMAx Douglass. 



Geddes aad Thomson, " The Evolution of Sex, ' p. 23. 



