1923 ENTOMOLOGICAL SOCIETY. 31 



offered may be of assistance to some one who has both the time and inclination 

 to investigate and reach more definite conclusions in the problems which are 

 as yet but slightly known. An attempt has been made to limit technical 

 phraseology to the minimum. Certain obvious facts stand out above all others; 

 we have yet to furnish the details and connections. 



In discussing the relationships which exist between the immature stages 

 of insects, and the value which their study may be to the taxonomist, it is 

 necessary to first consider in general the prevailing views which are held by prom- 

 inent entomologists at the present time. It is almost impossible to draw 

 any separating line between the two schools of thought if we consider them as 

 "schools," for the reason that there is complete intergradation. The one extreme 

 holds that the immature stages are an adaptation for the purpose of distri- 

 buting the various members of the insect world over all the available food 

 plants, and thus guaranteeing against the extermination of plants which might 

 be most desirable as food. Therefore, it is argued, the immature stages, being 

 secondary, cannot indicate relationships of the adults to any great extent. The 

 other view is that the immature stages are a direct indication of relationship. 

 Various modifications of both views exist, and it is very doubtful if any entomo- 

 logist today holds either extreme as practicable. Rather there is a tendency 

 toward an equal balance between the two, and this would seem to be the obvious 

 basis for all studies pertaining to a stable classification. 



So many factors enter into a study of this nature, many of them wholly 

 conjectural, that one must advance with the greatest caution. What may 

 be considered as a definite group of causative factors bearing upon the develop- 

 ment of one tribe of insects possessing similar biological habits may not apply 

 or must be greatly modified in another tribe having very similar immature 

 stages yet possessing definite though small differences in the imagines. It 

 has been argued by many, among them some of the foremost students of zoology, 

 that a character, once lost, can never be regained. If such were the case the 

 problems confronting us in the systematic arrangement of insects would be very 

 simple in their solution. We may consider that a character lost through the 

 various environmental conditions will never recur as long as those conditions 

 exist, but the whole scheme of nature is so complex that the very causes which 

 brought about the change are themselves altered because of changes involved. 

 Life in one form reacts upon life in another form, animal life upon vegetable 

 life, vegetable life upon animal life, animal upon animal and vegetable upon 

 vegetable. To exemplify this well-known but always remarkable phase of exist- 

 ence, it is merely necessary to point c.'t that a superabundance of a given 

 species of plant life induces an abundance ^f enemies, both plant and animal, 

 else the plant species would develop to such an extent that other plants would 

 find life impossible. 



In the case of life the prime object is the perpetuation of the species. The 

 result is that environmental influences bear upon insects in such a way that 

 they always react to the slightest changes either in food or temperature. Such 

 changes may or may not be sufficiently marked to cause the fauna or any one 

 member to become specialized to such a degree as to be quite distinct from its 

 ancestors of many generations previous. If certain environmental conditions 

 are more or less local, and do not cover the whole range of a species what is 

 considered a new or distinct species may be developed. 



It seems reasonable to suppose that similar environment will, in many cases, 

 develop stimuli along certain lines in more than one species of insect, indeed 

 in insects belonging to moderately or widely separated groups. Where the 



