REPORT OF THE ENTOMOLOGIST. 187 



material. Only about fifty years ago the number of named insects 

 did not exceed 75,000 species; while at present fully five times that 

 number are represented in named and arranged collections. The ac- 

 tivity of the past half century among entomologists has been great, 

 still not sufficiently so to keep apace with the accumulating material 

 from all parts of the world. Judging from our present knowledge, 

 and from the vast extent of the globe, which is still terra incognita in 

 national science, it is not at all improbable but that the number of 

 species will reach a full million. This too seems the more probable 

 when we take into consideration that thus far only the comparatively 

 large and more common forms are known. 



If the distinct species of insects are so numerous as to be almost in- 

 comprehensible, what can we say of the individuals of some of the 

 commoner and more injurious species? Dr. Fitch has given us a com- 

 putation of the number of cherry tree aphids occurring upon trees grow- 

 ing on his grounds. These figures are recorded in his first and second 

 annual reports on the insects of New York, page 127, where we find 

 the following : "Among the cherry trees alluded to was a row of seven 

 young ones which had attained a height of about ten feet. By count- 

 ing the number of leaves upon some of the limbs, and the number of 

 limbs upon the tree, I find a small cherry tree of the size above stated 

 is clothed with about seventeen thousand leaves. These leaves could 

 not have averaged less than five or six hundred lice upon each, and 

 there was fully a third more occupying the stems and the tips of twigs. 

 Each of these small trees was, therefore, stocked with at least twelve 

 millions of these creatures." Now, if these figures only represent 

 the number of individuals of this one insect upon seven small trees, 

 what can we imagine the number of individuals to have been through- 

 out the entire country? The chinch bug, Rocky mountain locust, 

 Colorado potato beetle, Hessian fly, wheat midge, and like insects are 

 other examples of how numerous in individuals a single species of in- 

 sect may become during years of their greatest abundance. 



PECULIAR AND VARIOUS MODES OF REPRODUCTION, AS WELL AS 

 GREAT FECUNDITY AMONG THE DIFFERENT FORMS OF 



INSECT LIFE. 



Among the mammals, birds, and other vertebrate animals, the 

 modes of reproduction are very similar throughout each of the classes. 



