518 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



forms could not be examined with the hand lens, led inevitably to the result that 

 the interests of entomologists were long centered upon these larger and aestheti- 

 cally more i^leasing insects. The minute, dull-colored, and, to the unaided eye, 

 unimpressive forms — actually perhaps the majority of insects — have always been 

 much neglected and it is only in comparatively recent times that most of them 

 have begun to attract any special attention. Even today only a relatively small 

 number of entomologists concern themselves especially with such forms. 



As long as entomology remained primarily an expression of aesthetic feeling 

 this neglect was general. Then, with the growing appreciation of the economic 

 and biological interest of many of these small forms, their study began to ex- 

 pand. The economic importance of the scale insects (Coccoidea) and other small 

 pests of agriculture and the recognition of the importance of the sucking lice in 

 the transmission of disease led to the study of these groups and this interest has 

 spread to other small forms. Even so, the microscopic insects — to which may 

 arbitrarily be assigned insects less than five millimeters long — have never re- 

 ceived the attention they deserve. 



Apart from purely aesthetic considerations, the difficulty of studying these 

 minute forms has been a determining factor in causing this neglect. They can- 

 not be studied satisfactorily from pinned specimens, even from specimens 

 mounted on minute pins or points and even with the aid of the improved micro- 

 scopes which we possess today. They require special methods in making prep- 

 arations that can be examined by transmitted light under the powers of the 

 compound microscope. Onlj^ as these methods have developed could any real 

 understanding of such forms be gained. 



Throughout his entomological career the writer of these lines has been inter- 

 ested almost exclusively in these microscopic insects. He must confess to being 

 irritated by any insect on a pin; why not mount it on a microscope slide, where 

 it is possible to see what is actually on the insect, if the preparation be properly 

 made"? His interests have been largely confined to insects which must be so 

 mounted if they are to be studied at all with any degree of satisfaction. More 

 than thirty-five years of experience with the scale insects and the two groups 

 of lice, with an occasional excursion into other groups of small forms, has served 

 only to increase his impatience with insects which cannot be so studied. If the 

 whole insect is too large to go on a microscope slide, it can be divided so that 

 its parts can be so mounted. Even students of the Lepidoptera, in spite of their 

 reluctance to "ruin a specimen," have learned to place the genitalia of the males 

 upon microscope slides. But still the great majority of all insects, almost re- 

 gardless of their size, are mounted on pins, even though little can be learned 

 from such specimens. It is quite true that for the larger forms this is probably 

 the quickest way to prepare them and possibly the easiest way to study them, 

 but even such forms must sometimes be torn to pieces and reduced to a condi- 

 tion in which microscopic study is possible. Naturally no one would advocate 

 attempts to put Morplio butterflies on microscope slides! But, after all, 

 large forms like these and the rhinoceros beetles are not all the insects. There 

 are whole hosts of minutes flies, minute beetles, minute parasitic Hymenoptera, 

 and many other groups which can best be treated as microscopic insects should 



be treated. 



Along with this matter of properly preparing specimens for study goes the 



