124 TKANSACTIONS OF THE ILLINOIS 



Studied. All the synopses and descriptions of insects or groups of 

 insects presuppose the presence of a whole specimen. If you will try to 

 fix the germs of a fossil hickory-leaf by using an ordinary manual of 

 botany, you will appreciate the perplexity of the student who attempts to 

 determine by the study of a crushed and mutilated head the number of 

 segments in the abdomen, or to decide whether the paraglosscs are con- 

 nate with the ligjila when he has nothing but a mandible to go by. The 

 heads of beetles are, however, usually well enough preserved for study, 

 and the mouth-parts are structures of great variety and complexity, and 

 can commonly be made to solve the question of family and often of 

 genera also. I consequently had mounted at the laboratory, for reference, 

 a large number of slides of mouth-parts of all the families of Illinois 

 insects of which we had specimens for dissection. By a careful collection 

 and arrangement of the mouth-characters used in the descriptions of 

 families, I constructed a key to the families or groups of families of 

 beetles, based upon these head-characters only. This has proved very 

 useful in settling doubtful cases. 



I soon found that the Thrushes ate more largely of Carabidae (pre- 

 dacious ground-beetles) than of any other Coleopterous family — these 

 constituting nearly one-third of all the beetles eaten. The determina- 

 tion of their genera, therefore, became unusually important. To this 

 end I dissected and mounted the mouth-parts of all the Illinois genera in 

 our collection, usually several species of a genus, and by an original 

 study of these constructed a set of analytical keys, by whose aid I have 

 found it easy, usually, to classify the Carabidae. These keys, being at 

 present incomplete, have never been relied upon solely, but have been 

 used with caution merely as clues to the determination. I have now most 

 of the material in hand for the completion of these keys, and shall print 

 them hereafter. 



Another serious perplexity arose when the attempt was made to fix 

 the economical values of the different insects encountered, since to do 

 this as well as it ought to be done required a complete command of the 

 whole subject of economical entomology; a command so ready as to 

 enable one to bring to bear upon any genus or species the whole body of 

 our knowledge relating to it. If I had been a thorough specialist in 

 economical entomology, which I am very far from being, I should have 

 hesitated to form exact opinions on these matters without a review of the 

 literatum of my specialty, since we are so likely to give undue prominence 

 to the facts of our own observation, or to those which have most recently 

 come to our knowledge. Under the circumstances such a careful 

 scanning of the literatum of the subject was indispensable, and I there- 

 fore commenced, and have well under way, a complete index to all the 

 most important published matter in this department, including the works 

 of Harris, Fitch, Packard, Walsh, Riley, Le Baron and Thomas. This 

 index contains not only references to every fact stated respecting the 

 injury or benefit attributable to any insect or group of insects, but also 

 compact statements of the facts themselves, so that when finished it will 

 form a nearly complete compend of the economical entomology of this 



