1915} Quantitative Entomology 381 
There are over 10,000 species of insects recorded in Cali- 
fornia. Of these not over 1000 are found in many collections. 
or known from any large numbers of localities. In none of the 
9000 is there sufficient data at hand or liable to be secured to: 
assist in solving any of the problems of geographical distri- 
bution. Nor do any of them play any important part in bio- 
logical problems, unless it be the problem connected with the 
maintenance of existence by rare species. 
If only in the neighborhood of 10% of the insects contributed 
much to our knowledge of distribution it is probable that 1% 
includes all those whose abundance causes them to play an 
important part in the ecological relationships or in economics. 
We must devise means of expressing the dominance of species 
perhaps in terms of their relative frequence of individuals or 
relative mass and for ecological purposes it might be better 
expressed in terms of food consumption as related to its dis- 
tribution in regions, in special habitats or in seasons. The 
idea is that we have only touched some of the exterior details on 
the surface of the subject and must develop means of studying 
the quantitative significance of distribution in order to arrive 
at the real meaning of the subject. 
But it will not be necessary to follow this idea through all 
the departments of entomology to the study of Physiology, 
Development or Life History, adaptations and the various other 
departments of ecological study. One will see at once that the 
same need of a definition of the elements of the subjects, their 
subdivision and classification until we can express differences. 
quantitatively with quite rigorous accuracy will open the way 
to a new and loftier conception of our subject and in con- 
clusion I wish to point out some of the changes this line of 
development is beginning to produce in economic entomology 
and particularly to the portion which might be called Horti- 
cultural Entomology. 
Economic Entomology has gone through remarkable changes 
of viewpoint. Half a century ago the subject would have been 
defined as the study of injurious insects. After the remarkable 
series of discoveries in the seventies and eighties of our whole 
series of efficient insecticides, the thought of entomologists so 
changed that the subject might have been defined as treating 
of the methods of killing injurious insects. Now the emphasis 
