70 PROC. ENT. SOC. WASH., VOL. 23, NO. 4, APRIL, 1921 



stupid depends almost entirely upon his ability to extract from 

 the storehouse of his subconscious mind the appropriate or 

 necessary impression or thought at the psychological moment. 



That illustrations are potent in evoking mental impressions 

 must be obvious to all observant persons, and naturalists, 

 especially, will readily admit the important part played in the 

 natural sciences by well drawn illustrations. The most obvious 

 function of such illustrations, of course, is their explanatory 

 office. They aid the imagination in visualizing the subject 

 treated. But illustrations have another equally valuable 

 function regarding which we seldom think, namely: The fixation 

 in our memories of the gist of the related text; in other words, 

 they render available through the association of ideas those 

 memory complexes containing all we know regarding the sub- 

 ject illustrated. Illustrations therefore must necessarily have 

 played a most important role in the remarkable advance of 

 applied entomology which has taken place in the United States 

 during the past century. 



In spite of the many mechanical and other refinements that 

 photography has undergone during the past forty years, it has 

 not yet reached a stage where it is possible by that means to 

 produce truly satisfying representations of most insects, and 

 especially where magnifications of more than a few diameters 

 are required. Photography, of course, is an invaluable aid to 

 entomology in many ways, especially for the purpose of showing 

 pathological changes due to insect work or the environmental 

 atmosphere of the species under discussion, but its limitations 

 in recording the insects themselves are perfectly obvious. It 

 is difficult, if not impossible, even in the case of large insects, 

 to reproduce them by photo-engraving methods alone, in a 

 manner approaching the crisp, clear image limned by the 

 human hand with the aid of pen and ink, and pencil. The 

 mental impressions left by the perception of most published 

 photographic representations of insects may be compared with 

 those produced by eating unsalted food. One immediately 

 recognizes the fact that something is missing, but fails to per- 

 ceive for the moment just what the missing element is. This 

 feeling of dissatisfaction proceeds, I believe, from the absence 

 of the vivid image as produced, in the line drawing, by the per- 

 fectly black line on the clear white paper; a sparkling effect 

 which no other method of illustration has yet been able to equal. 

 Another factor which tends to make drawings more acceptable 

 than photographs, especially to entomologists, is the custom 

 observed by the best draughtsmen of emphasizing, to just the 

 right degree, those cardinal characters of the model which are 

 recognized by the eye as constituting the habitus of the insect. 

 This, of course, is the principle of caricature exercised in a modi- 

 fied degree. Photographs may indeed record habitus, but very 



