142 PROBLEMS OF GENETICS 



the omnipotence of Selection must frequently find themselves 

 in this dilemma. 



Taking the evidence as a whole, we may say that it fairly 

 suggests the existence of some connection between modern urban 

 developments and the appearance and rise of the melanic vari- 

 eties. More than that we cannot yet affirm. It is a subject 

 in which problems open up on every side, and all of them are 

 profitable subjects for investigation. Unhappily such animals 

 are difficult to rear successfully in captivity for many generations, 

 owing to their extreme liability to disease. Not the least in- 

 teresting feature of the melanics is the fact that the black vari- 

 eties provide about the best and clearest example of a new dom- 

 inant factor attaching itself to a wild species in recent times. 

 None of the cases are satisfactorily recorded or analysed as yet, 

 but the evidence is clear that doubledayaria is a dominant to its 

 type, and in several other dark varieties, though the pigment 

 deposited is not black, the records show that the increased 

 amount of the pigment almost certainly is due to a positive factor. 

 Of this, Hemerophila abruptaria is a good example. 24 There are 

 some irregularities in the results, but taken together they leave 

 little doubt that the dark brown variety is a dominant and the 

 light, yellowish brown a recessive. 



A curious parallel to the rise of the melanic moths in England 

 is provided by the case of the Honey-creepers or Sugar-birds, 

 in certain West Indian islands. 25 These birds of the genus 

 Coereba (Certhiold) range from Southern Mexico to the Northern 

 parts of South America and through the whole chain of the West 

 Indian islands and Bahamas except Cuba. There are numerous 

 local forms, and many of the islands have types peculiar to them- 

 selves, as is usual in such cases. Some of the types or species 

 range through several islands, but according to Austin Clark 26 

 no island has more than one of them. Cory 27 reckoned twelve 



24 See Harris, Proc. Ent. Soc. London, 1904, p. Ixxii, and 1905, p. Ixiii; also 

 Hamling, Trans. City of London Ent. Soc., 1905, p. 5. 



25 1 am indebted to Mr. Outram Bangs of the Harvard Museum for calling my 

 attention to this remarkable case. 



26 Auk, 1889, VI, p. 219. 



27 Ann. N. Y. Acad. Sci., 1878, I, p. 149. 



