2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



for analyzing an insect in an orderly way from one end to the other. 

 Incidentally it should be observed that the results come out the same 

 regardless of which end is taken first, and this in itself is presumptive 

 evidence of the soundness of the proposed solution. Of course, it 

 may not be claimed that an orderly concept of the structure of an 

 animal has, in itself, greater claim to truth than one that is prolix, 

 unless it can be demonstrated that orderliness, and consequently sim- 

 plicity is a fundamental law of animate nature. It is possible that the 

 value of simplicity has been overestimated, and that too much con- 

 fidence is raised in its favor by its mere reputation. We may concede 

 that simplicity is the soul of wit, the essence of art, a distinguishing 

 mark of virtue, etc., but when simplicity comes to be regarded even as 

 an index of truth itself, we must look upon its claims with some 

 suspicion. Simplicity, however, does have in all things a convincing 

 manner. 



Segmented animals, as every zoologist admits, are composed of a 

 series of segments, and there is no dispute that the segments were 

 most probably at one time alike. Hence, it follows that each seg- 

 mentally composite section of the animal's body has the same basic 

 and fundamental structure, a principle which also no one denies. 

 Diversities of opinion concerning the correspondence of parts in dif- 

 ferent body sections, then, are merely matters of difference of 

 interpretation. 



In the study of insect anatomy entomologists have examined the 

 insect's head as if it were a thing in itself, having only a cervical 

 continuity with the rest of the body; they have minutely explored 

 and topographically mapped the thorax, but have for the most part 

 looked upon it also as a discrete entity ; they have painstakingly in- 

 vestigated the abdomen, but without giving much thought to aligning 

 its parts with those of the thorax and the head. Students in entomology 

 are taught in this sectional manner, textbooks are written in the same 

 disjointed style. In short, the first principle of insect anatomy is that 

 an insect is divided into head, thorax, and abdomen. As a consequence, 

 ideas concerning the unity of the insect are vague at best, and collec- 

 tively are little short of chaotic. 



For a number of years the writer has been attempting to discover 

 the basic plan of arthropod organization that is repeated through the 

 segments, and to see how the special modifications in the several body 

 regions of the insect may conform with the structure of a theoretically 

 generalized segment. The results are quite simple, and are derived 

 from following the horizontal constructional lines through the entire 

 segmental region of the trunk. This scheme for studying the insect 



