March, 1914.] 49 



from a particular point of view and with great care to avoid illusions. 

 Besides this, they almost all turn upon questions of degree — a little 

 more or a little less, &c. — and are absolutely incapable of being 

 defined in language which shall cover all cases. No possible Tables 

 founded on them can ever make the determination of the species easy 

 even for an expert, much less for a beginner: and practically it is by 

 characters of coloration only that most actual determinations are made. 

 These latter characters are generally recognised with little difficulty ; 

 but it is certain that some of them are liable to variation, and to what 

 lengths such variation may go within the limits of any particular 

 species, it is as yet quite impossible to say ; we know only that among 

 the few forms exhibiting well-marked peculiarities of structure there 

 seems to be almost unlimited variability as to colour, but, if we refuse 

 in other cases to accept colour-characters as " specific," it will be 

 impossible? to distinguish "species" among them at all! Perhaps it 

 is needless to point out that no division of forms into species, varieties, 

 and so forth, which rests entirely on the observation of likenesses and 

 unlikenesses, whether of structure or colour, among cabinet-specimens 

 (picked up here there and everywhere by collectors in various districts) 

 can be more than 'provisional, in the absence of any evidence as to th e 

 occurrence of pairing between particular <$ J and $ ? , or as to the 

 descent of particular groups of specimens from a common stock, or as 

 to the attachment of different forms to different food-plants, &c. And 

 unfortunately in the case of Tenthredopsis forms, such external evi- 

 dences as to their consanguinity are at present hardly ever to be 

 obtained. Of most of our reputed species no form is known except 

 the imago ; no one is known to have reared even a single brood of 

 them ; pairings between what we assume to be their sexes have never 

 been recorded ; in short we are absolutely ignorant of any fact of 

 their actual life-history which might suggest affinities with other 

 forms, and only believe them to be " species," because specimens of 

 them agree in a certain number of " characters," which we believe in 

 this particular case to be constant, though we have no positive proof 

 that they are so ! 



The remedy for these evils is obvious. If we are ever to arrive at 

 anything approaching finality in classifying and naming Tentkredopsis 

 forms, we must find their larva), food-plants, <fcc, and learn how to 

 rear them through successive generations, noting and recording all 

 indications that any of their characters are or are not constant: we 



B 



