46 
AVERAGE CHARACTERS AS EXHIBITED BY SPECIES. 
As I have already pointed out, the amount of variation that occurs 
m each species, year by year, is much greater than was originally 
supposed, and yet, the weeding out of the most marked aberrations results 
m the production of what may be called a general facies, presenting an 
average of the special characters, for each particular species. In 
spite, therefore, of the variation that exists between the individuals of 
a species, a similarity is preserved which enables the species to main¬ 
tain itself in its given environment. 
INDIVIDUALS OF A SPECIES NOT IDENTICAL. 
W hen the materials acted upon are identical, and the conditions 
under which they are acted upon are identical, we may take it as a 
general axiom, that the same cause will produce similar results, 
l>ut in the true sense of the word, the individuals of no species ai’e 
identical, and hence the same cause acting upon the individuals under 
the same conditions does not produce the same results, except in a 
very general manner. Bearing this in mind, we may proceed to the 
consideraton of a few special phenomena that have proved interesting 
to me. ° 
ON THE ORIGIN OF VARIETIES OR LOCAL RACES. 
We may make the general statement, subject to the above limita¬ 
tion that uniformity in environment tends to produce a general 
uniformity in the species; whilst, great differences of environment 
tend to produce great differences in the species. Many species of 
Lepidoptera bearing out this general statement will occur to all ento¬ 
mologists, yet it is not difficult to mention species whose appearance 
suggests antagonism to the general principle here enunciated. 
The well-known Pyrameis cardui has an almost cosmopolitan range. 
It exists under a variety of physical and climatic conditions in both the 
Old and New World, yet it is a species that varies little. As a matter 
of fact, in spite of the apparent dissimilarity of its habitats, these 
are comparatively alike. The species inhabits the sub-tropical and 
warmer temperate regions of the world. Hence the climatic conditions 
are not unlike. From these areas it is a wanderer, and has no lasting 
habitation in the colder regions, of which it is reported to be a native"! 
Its habits are similar all oyer the world. By the swiftness of its flight 
it escapes from its enemies, and, on a flower-head, at rest, it is 
sufficiently protected to be difficult of detection. Variation in its 
colours would be of no service to the species ; hence, in spite of its 
wide range, there is no attempt to set up local colour variation. The 
Australian form, hceivatin, shows a tendency to develop a transverse 
row of ocellated spots on the hind-wings. Now and again a striking 
aberration may be bred or captured, but these do not amount 
perhaps, to one in a million, and do not affect the general question! 
IIoio, then, w 7 e ha\e an instance of a species in which variation in hue 
would be of little or no use to it, and we find as a result that its colour 
and markings arc very rarely modified, whatever may be the conditions 
of its environment. 
Let us now consider for a moment, a species that depends not upon 
its swiftness of flight, but upon its colour and markings, for its safety. 
No better example can be selected than Amphidasys betularia. Its pal© 
grey-white colour, plentifully peppered with black dots, forms about as 
useful a pattern as ono can well imagine for the protection of this 
