92 SECTIONAL ADDRESSES 



birds, and of the dried insects reveal to him the latitude and the kind of 

 variability and variation in the species of which he has adequate material, 

 and enables him to compare results with the biologists who have studied 

 the flexibility of species with the view to ascertain whether the variability 

 is purely fortuitous or whether there is system in the apparent confusion, 

 many so-called laws of development having been discovered in the course 

 of such inquiries. Now, according to the experience of the systematist, 

 such laws are rules with exceptions, sometimes the normal and the 

 exceptional balancing each other, and it may be stated in general that 

 the opposite must always be expected to occur. That is somewhat dis- 

 tressing, but very true to living nature, where there is little need for logic 

 and where the mathematical constant expressed by ' one equals one ' does 

 not hold good, as any farmer can tell you. Exceptions have a certain 

 fascination, not only for the writers of novels and plays, which are mostly 

 based on exceptional characters or exceptional situations, but also for the 

 biologist. As exceptions are comparatively rare, it requires large collec- 

 tions or long observation to discover them, and if there is no known excep- 

 tion to a certain rule of development, one has the feeling that it will some 

 day be discovered. Take as an instance the bright colouring found among 

 birds and butterflies. In sexually dimorphic species the male is the 

 brighter coloured as a rule, but there are also butterflies and moths in 

 which the female bears the gayer garb, this being particularly often the 

 case in mimetic species, where conspicuousness plays an important role, 

 such as Archonias hellona ^ and Hibrildis tiorax} An interesting case of 

 exceptional difference in colour and behaviour among birds and another 

 among moths may be mentioned in this connection. In the swift moth 

 of our meadows the white (^ dances up and down a foot or two above the 

 ground, keeping to the same spot and being in the twilight a very con- 

 spicuous object. The dark-coloured fernale, barely visible as it slowly 

 booms along in search of a mate, does not take the first male it encounters, 

 but makes a selection, there being evidently a difference in the males not 

 noticeable to our dull senses, probably a difference in scent, the ^(^ 

 having the hindleg converted into a scent-organ. That the male makes 

 itself conspicuous agrees well with the general behaviour of that sex in 

 animals, but that the female takes the initiative is an exception. A 

 parallel instance occurs among Gallinaceous birds ; among these game- 

 birds are found the most striking instances of sexual dimorphism, the 

 cocks exhibiting an often marvellous display of colours, as in the Peacock, 

 Pheasants, Fowls and others, the females being comparatively incon- 

 spicuous. It is therefore somewhat startling to find just in this order 

 a genus in which the colours and behaviour of the sexes are reversed. 

 In most species of the Oriental genus Turnix, a kind of Quail, the females 

 are larger than the males, bear a much brighter plumage, utter the call- 

 note, fight each other for the possession of a male, and leave it to the male 

 to incubate the eggs and to take care of the young— a state of civilisation 

 of which we notice the beginnings in the human race. It is rather odd 

 that in this instance the weaker sex, the male, attends to the young. For 



1 ^ Cramer, Pap. Ex. I., tab. 13 (1775) ; f. id., I.e. ii, tab. 177 (1779). 

 ^ Cf. Poulton, Trans. Ent. Soc, 1928, p. 380. 



