20 NORTH AMERICAN DIPTERA 



so-called races (supposedly geographie forms) are developed. In such 

 cases connecting or transition forms usually occur and it is almost 

 always true that the races, say northern and southern, are connected 

 in the intervening region by a perfect transition of the characters of the 

 two races. Races are interesting but it is not necessary to give them 

 names. Moreover, "variety" was used in the same sense long before 

 people thought of "races" for biological classification and 1 think we 

 may extend the law of priority and use it in this sense, thus eliminating 

 "race" and "sub-species". 



The naming of aberrations, transition forms and sucli things should 

 be beyond the pale in true science and such a practice must eventually 

 result in ridicule of the science as a whole. It is, of course, verj^ neces- 

 sary to call attention to tliese forms but to name them is utterly 

 needless. Knowledge of them is essential in tracing out the relation- 

 ship and development of species, and of great interest, too, but we 

 should not lose our perspective and attach exaggerated importance to 

 names. 



How to Use the Keys 



The use of keys is not a difficult matter l)ut there may be some who 

 have not had experience with them. Some keys may not be altogether 

 simple and may not run as smoothly as others. To find the genus to 

 which your specimen belongs turn to the table of families (on the 

 following page) and read over couplet 1. Two alternatives are given: 

 the insect must go in either section. If it has large wings you go to 

 couplet 2 and you repeat the process until it is found that your s])eci- 

 men comes to a section where it agrees with the diagnosis ending in a 

 family name. You have now found the "family", but to be sure read 

 over the other alternative so that the characters in both may be checked. 

 Now turn to the family indicated and continue in the same way until 

 tlie genus is reached. 



It sliould be remembered that keys are merely guides and the fact 

 that a species traces out to a certain ])lace in a key is no guarantee that 

 it actually belongs there. If one is familiar with the genera of a family 

 he may be reasonably certain either that tlie insect belongs where it 

 traces or that it is quite different; in either case he should check with 

 descriptions of genera not included in the key or with the genus in- 

 cluded, either by means of determined specimens or with the generic 

 description. If a specimen does not seem to agree with the genus to 

 which it traces check back and try one of the other alternatives since 

 there may have been an error in interpretation of the characters used 

 or the specimen may be one that is somewhat aberrant. 



