928 . The American Naturalist. [October, 
colors), the writer passes to the uses of colors, the chief object of this 
inquiry. 
Mr. Poulton supports his own theory of the direct physiological 
value of the uses of color to animals by a large amount of experi- 
mental evidence brought together from many sources. Some interest- 
ing conclusions were brought forward by Lord Walsingham upon the 
predominance of dark varieties of insects and white varieties of birds 
and mammals in northern latitudes. The most widespread use of color 
appears to be its assistance to an animal in escaping from enemies 
and in capturing prey; the former is called Protective, the latter 
Aggressive Resemblance. 
The general recapitulation of the colors of animals gives (1) non- 
significant colors; (2) significant colors, which are subdivided into 
colors of direct physiological value, protective and aggressive resem- 
blance, protective and aggressive mimicry, warning colors, and colors 
displayed in courtship. Mimicry is an important section of special 
resemblance; when an animal gains advantage by a superficial resem- 
blance to some other species which is well known and dreaded, because 
of some unpleasant quality, it is called protective mimicry; when, 
however, an animal resembles another so as to be able to injure the 
latter, the mimicry is considered aggressive. 
Warning colors are advantageous to enable an animal to escape 
experimental ** tasting,” for, when it possesses an unpleasant attribute, 
itis well to advertise the fact as publicly as possible by conspicuous 
patterns and strongly-marked colors. 'The colors and markings of 
butterflies and moths often represent some familiar appearance of 
withered or decayed leaves. A detail of great interest is added to the 
disguise by the semblance of a small hole to indicate piercing by 
insect larvae. Mr. Poulton allows himself to say that perhaps the most 
perfect concealment attained by any butterfly is seen in the genus 
Kallima, described by Wallace. This resembles in outline a withered 
and somewhat shriveled leaf, when at rest ; along the supposed leaf 
runs a distinct mark like a mid-rib, with oblique veining on either side. 
The color and markings of birds’ eggs are supposed to be of high 
protective value as observed in their natural surroundings. 
Some remarkable instances of rapid adjustment are cited in the 
chapter on *' Variable Protective Resemblance in Vertebrata,’’ etc. 
Fishermen know that trout caught in a sandy-bottomed stream are light 
colored, while those caught in a muddy stream are dark, ‘It is also 
well known that the same fish will soon change in color when it passes 
from one kind of background to the other." Other animals possess the 
