D.— ZOOLOGY 93 



it would surely be safer for the chickens if the stronger parent took 

 charge of them, for the sake of defence ; but perhaps the heavy hand, or 

 in this case, the strong beak, is, in the bringing up of the young, not 

 always superior to gentler means of persuasion. In the Struthiiformes 

 we find likewise that the male attends to incubation and to the nursery, 

 with the exception of the African Ostrich, where both sexes incubate 

 alternately, as is the rule in birds. As an example of birds of which only 

 the female incubates we mention the Hornbills, the male ensuring the 

 continuity of incubation by so blocking up the entrance to the hole con- 

 taining the female on the nest that the female cannot get out. During the 

 whole period of incubation and until the young birds are fully fledged the 

 male feeds the female and young through the minute hole in the plastered- 

 up nest opening. Of the two classes of animals which I have studied 

 more particularly, birds and Lepidoptera, the coloration is on the whole 

 more constant in birds within the species at the same locality, apart from 

 differences of sex and age, than in butterflies and moths, and individual 

 di- and polymorphism is decidedly more common in the insects than in 

 birds, but it is by no means absent among the latter. Dark and light 

 phases long known to occur regularly among certain raptorial birds — • 

 for instance, harriers — have during recent years been discovered to exist 

 also here and there in other groups of birds, where they have formerly 

 generally been described as distinct species. Such a correction had also 

 to be made in the systematics of the American genus RJtamphocoelus, 

 where red and yellow forms differing only in colour are now regarded as 

 being individuals of one species, intermediate examples of an orange colour 

 also being known, as well as very exceptional examples, such as the aberra- 

 tion Rhamphocaelus dunstalU Rothsch., in which the red and yellow colours 

 extend to parts of the body other than those normally so coloured. The 

 gaily-coloured parrots furnish other examples of dichromotism ; for 

 instance, the parakeet Eos fuscata Blyth, which is a fairly common bird 

 in New Guinea, appears in a red and a yellow form in the same place, 

 both forms being about equally frequent, the red one slightly prepon- 

 derating, and the lory Charmosyna stellee Meyer, which appears in a black 

 as well as a red form. This replacement of red by yellow recalls numerous 

 Lepidoptera in which a similar change of colour takes place. Sometimes 

 this change is sex-linked, the male being red and the female yellow, or 

 the male yellow and the female red, the one happening about as often as 

 the other ; the same is true of the change from orange to yellow, and from 

 yellow to white. Pierine butterflies of the genera Teracolus, Pereute, 

 Anthocharis may be mentioned. Occasionally species are found which, 

 independently of sex, regularly occur in red and in yellow individuals, 

 or in yellow and white ones, red specimens being on the whole more 

 frequent than yellow ones, or yellow specimens than white ones — as, for 

 instance, in Papilio deiphobus L. and P. deiphontes Feld., from the Moluccas, 

 and the Agaristids ^ Xanthosptlopteryx karschi, X. africana and Rothia 

 eriopis, from Africa. The colour scale red, orange, yellow, white agreeing 

 with the sequence in the ontogenetical development of the colours in the 

 wing of the Lepidopteron, an acceleration of the physico-chemical process 

 3 Cf. Seitz, Macrolep.. vol. xv, p. 38 ff. (1913)- 



