2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. J^J 



INTRODUCTION 



There are no facts of structure presented in this paper that are 

 not recorded elsewhere ; but a mere lack of new information should 

 not be held to lessen the value of a piece of work, or to make it un- 

 worthy of scientific consideration. Facts are the food of science, 

 and, like all food, they do not contribute to growth of the body 

 until digested, distributed, and assimilated. 



It is time for entomology to be taking stock of what it has ac- 

 quired, to assemble its facts, and to get them into form that will 

 facilitate progress, dropping a few old ideas, if necessary, and taking 

 on a few new ones. A science, in its growth, is likely to be some- 

 thing like a caterpillar — it increases rapidly during a period w'hen 

 its skin is soft and elastic, but after a while it begins to become hide- 

 bound in its own cuticula ; then the old skin must be cast ofif, and a 

 new one formed that will again allow of growth and development. 



A mere review of the known facts on any particular subject, 

 scattered as the records are likely to be through many scientific journals 

 and presented often in highly technical language, may render at 

 least the double service of making the facts more easily available 

 and of showing more plainly the bare spots of ignorance; but it 

 may, also, give an insight into general truths heretofore unrecognized. 



Concerning the anatomy of insect sense organs, and the intimate 

 structure of the insect nervous system, much is known, i. e., to those 

 who have studied the sense organs and the nervous system of 

 insects. To the general entomologist, little is known of these sub- 

 jects. A knowledge of mere structure, however, is of no use in 

 itself, it is only a prerequisite to a study of function. A knowledge 

 of insect physiology, furthermore, is still of no particular importance 

 until it helps us to understand the nature of the insect as a living 

 organism. An understanding of the nature of an insect, again, has 

 real significance only as it enables us to understand the nature of 

 life in general. So, everything we take up in science is of value, 

 in the minds of those to whom a knowledge of the universe is the 

 ultimate aim, only through the superstructure it supports. 



To the practical entomologist, however, the value of know^ledge 

 may be judged within more finite limits. The acquisition of any in- 

 formation that will help in the control of injurious insect species, 

 or that will further the propagation of useful or beneficial species 

 is to him in itself an end worth attaining. There can be no doubt 

 that the accomplishment of practical results in entomology will be 

 greatly facilitated when we have acquired a better understanding 

 of the physiology, the senses, and the tropisms of insects, and an 



