890 THE ZOOLOGIST. 
that it has come down as a survival to the present day in a host 
of instances to which we have applied the explanation of ‘ pro- 
tective resemblance.” The reason why it has thus survived is 
not because it contradicts, but because it does not require the 
modifying influence of natural selection. It neither broke the 
“law,” nor did it arise through the controlling action of the 
“law’’; and where species uninfluenced by the impulse of 
variation, or unharmed by a too rapid or excessive fecundity, 
existed in assimilative colouration to the surroundings which 
have remained unchanged, and subject to no climatic changes 
enforcing migration, such species have survived, and do appear 
to-day, in their original assimilative colouration. 
The suggestion receives support from many facts recorded by 
travellers and naturalists, which, taken singly, have only the 
appearance of curious observations, but, considered together, 
exhibit more cumulative force. According to Dr. A. Leith 
Adams, “there is, moreover, a seemingly strong disposition 
for the lower parts of animals to become white in winter, 1. e. the 
parts in closest contact with the snow; thus, the under surfaces 
of the Deer tribe are always whitest.”* Mr. J. Newton Baskett 
would seem to favour the same suggestion with regard to the 
colour of birds’ eggs :—‘“ To my mind the suggestion comes that 
many of our early birds with spotted eggs may have reverted 
from green and dead grass nesting to shingly or brilliant pebbly 
regions, carrying with them the bluish, greenish, creamy, or drab 
grounds, and by that tendency to variation for which we can 
never account—a thing as mysterious as life itselfi—they here, 
through the agency of natural selection, began a mottled colour- 
adaptation which has developed so highly in our shore birds, 
Gulls and their relations.”t The well-known and much-quoted 
observation made by Canon Tristram in North Africa cannot be 
omitted here :—‘“ In the desert, where neither trees, brushwood, 
nor even undulation of the surface afford the slightest protection 
to its foes, a modification of colour which shall be assimilated to 
that of the surrounding country is absolutely necessary. Hence 
without exception the upper plumage of every bird, whether Lark, 
Chat, Sylvain, or Sand Grouse, and also the fur of all the smaller 
* ‘Field and Forest Rambles,’ p. 124. 
+ Papers, ‘“‘ World’s Congress on Ornithology,” Chicago, pp. 97, 98. 
