24 PROBLEMS OF GENETICS 



tibiae are usually plain yellow. In both species there is a hori- 

 zontal yellow stripe on the thorax, but whereas in vulgaris this is 

 a plain narrow stripe, it is in germanica enlarged downwards in 

 the middle. These and other apparently trivial details of colour- 

 ation, though not absolutely constant, are yet so nearly constant 

 that irregularities in these respects are quite exceptional. Lastly 

 the genitalia of the males, though not very different, present 

 small structural points of distinction which are enough to distin- 

 guish the two species at a glance. 14 



In considering the meaning of the distinctions between these 

 two wasps we meet the old problem illustrated by the Sparrows. 

 The two species have somewhat different habits of life and we 

 should readily expect to find differences of bodily organisation 

 corresponding with the differences of habits. But is that what 

 we do find? Surely not. To suppose that there is a corre- 

 spondence between the little points of colour and structure which 

 we see and the respective modes of life of the two species is 

 perfectly gratuitous. We have no inkling of the nature of such 

 a correspondence, how it can be constituted, or in what it may 

 consist. 



Is it not time to abandon these fanciful expectations which 

 are never realised? Everywhere both among animals and plants 

 does the problem of specific difference reiterate itself in the same 

 form. In view of such facts as I have related and might indefi- 

 nitely multiply, the fixity of specific characters cannot readily 

 be held to be a measure of their economic importance to their 

 possessors. The incidence of specific fixity is arbitrary and 

 capricious, sometimes lighting on a feature or a property which 

 can be supposed to matter much, but as often is it attached to the 

 most trifling of superficial peculiarities. 



The incidence of variability is no less paradoxical, and without 

 investigation of the particular case no one can say what will be 



14 For an account of the distinctions between Vespa vulgaris and germanica 

 see Ch. Janet, Etudes sur Us Fourmis, Us GuSpes et Us Abeilles, n e , Note. Sur 

 Vespa germanica et V. vulgaris. Limoges (Ducourtieux), 1895; and R. du Buysson, 

 Monographic des Guepes, Ann. Soc. Ent. France, 1903, Vol. LXXII, p. 603, PI. 

 VIII. 



