GENERAL REMARKS. 99 



The ideal of a species will long be a subject of 

 thought to the biologist. Numerous have been the de- 

 finitions offered, but none can be said tersely to express 

 that which, in one sense, may be considered only as an 

 abstract thought. Sir Joseph D. Hooker, speaking of 

 plants, defines a species " as a collection of constant 

 varietal characters taken from any organ or part." 

 Another authority says, " When some general resem- 

 blance is combined with differences greater than such 

 as our experiences warrant us in attributing to mere 

 breed, we are obliged to regard the individuals as be- 

 longing to different species. But inasmuch as this 

 conclusion depends on the lack of evidence to the 

 contrary, and is far short of what is conceivably 

 possible to obtain, the tendency must be towards the 

 multij)licity of species." * 



Thus it happens that one thinker who lays too much 

 stress on minor details will form (say) forty-five species 

 out of our British brambles, whilst another, of greater 

 powers perhaps of generalisation, will reduce these 

 species to five alone. Botanists are still divided as to 

 the number of species that should be given to our 

 British willows. Still all biologists admit that species 

 do exist ; and that study can no more be carried out 

 without their recognition, than can arithmetic be 

 worked without its integers. 



At one time Darwin almost seemed to ignore species 

 as scientific entities, in such a phrase as " a species is 

 an arbitrary assumption convenient to the systematist " ; 

 and indeed his theory supposes that " all species are 

 descended from one progenitor." Nevertheless he 

 qualifies his above assertion by remarking that " they 

 (species) do not at any time or period present an in- 

 extricable chaos of varying and intermediate links. Yet 

 common is the error to make one out of the other." 



A highly suggestive and important illustrated me- 

 moir, on the structure of the terminal segment in 

 some small Hemiptera-Heteroptera, has comparatively 



=- Sir G. Stokes, Proc. Vic. Inst., 1883. 



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