( Ixvii ) 
in many insects, but also in many birds, the genera Merula 
and Corvus being examples. 
“Prof, C. William Beebe, Curator of Birds in the New York 
Zoological Society, published a most valuable paper in 1907 
entitled ‘Geographic Variation in Birds, with especial reference 
to the effects of humidity,’ in which he gave a full account 
of most instructive experiments carried out by him in the case 
of three species of American birds, a superhumid atmosphere 
having greatly increased the amount of black in the plumage 
in quite a short time. 
“In the same article Prof. Beebe refers to a paper by Mr. 
Seth-Smith in the ‘Avicultural Magazine,’ in which an attempt 
was made to show that Munia castaneithorax (one of the small 
Australian weaving-finches) was only a moist climatic phase 
of M. flaviprymna, which inhabits a much drier region ; he 
also reproduces the excellent plate which accompanied Mr. 
Seth-Smith’s paper, and which shows a complete series of 
intergrades between the two supposed species, several of which 
had come into existence after the importation of I. flaviprymna 
to this country. 
“ Mr. Seth-Smith believed that our moist climate had immedi- 
ately produced reversion to the chestnut-breasted type, a 
possibility quite conceivable if the birds were imported early 
in a wet summer, but I think not otherwise; for in 1907 I 
turned a pair into an outdoor aviary with very little cover, 
and one of these lived there throughout the moist winter of 
1907-8 without acquiring the slightest change of colouring ; 
so that heat, as well as humidity, seems to be a necessary 
factor. 
“Without question a great deal too much has been made of 
protective assimilation ; I believe myself that many creatures 
of related genera simply resemble one another because there 
has been no object in differentiating their colouring; their 
structure has been slowly modified, but the pattern and 
colours being more or less protective have been retained and 
even their tendency to vary has retained its impetus towards 
a fixed gradation in one direction ; so that in the /thomiinae 
we have a series of genera, all equally protected, the species 
in which are often remarkably alike. A similar case occurs 
E 2 
