326 The Mechanism of Evolution" in Leptinotaesa 



them will rest upon the interaction of the conditions of the medium and the 

 character of the factors or determiners, and their location, association in the 

 system, and capacity to react uniformly under a given set of surroundings and 

 associations. A most desirable result of the method of analysis and the deter- 

 mination of the interacting agents will be the passing of choice, selection, pur- 

 pose, utility, isolation, segregation, and the rest of the array of " biological 

 explanations " current in the literature as an " explanation " of the position in 

 closely placed habitats of forms, much alike but suflSciently different in minor 

 aspects to give true taxonomic value to them. 



Two main questions arise in this connection and can be successfully attacked 

 through experimental analysis : (1) In a given " species " or " race," in any or 

 all its habitats, does the actual germinal condition of the race differ in successive 

 generations, or is it constant throughout for the location and form ? (3) In dif- 

 ferent habitats does the constitution of the race change in constant, recognizable 

 gametic differences ? These are tests that should be made upon species or races 

 that are considered by the best of taxonomists as uniformly good species, which 

 are real things in nature. Eecognized geographical races are to be excluded from 

 this analysis, which is planned to reveal, if possible, whether in nature, separa- 

 tion into habitudinal groups of naturally miiform race may not begin in local 

 areas and be the result of processes that can be determined and utilized in 

 experiment. 



In the investigation of these problems I have used three methods of attack. 

 (1) The introduction of stocks from one colony into other isolated loca- 

 tions and the watching of the following generations and the recording of them, 

 to determine what they did in terms of the census-taker in the new locations. 

 This will give rather useful data with regard to the readiness of the stocks to 

 respond to different conditions, and also the direction and extent of the 

 response. (2) The transportation of samples of the materials taken at ran- 

 dom in the population from the locations under observation to some central 

 location, where all are reared in isolation under one set of conditions, and in 

 this manner can be tested the reality and permanence of the differences in the 

 populations from different locations. If the samples are random, and if the 

 breeding is in group culture, with no selection in the matings, then the result 

 will be an accurate demonstration of whether the differences present in the orig- 

 inal location are able to persist alongside of the differences found in other loca- 

 tions, when both are living under the same conditions. This I have tested by 

 taking the materials to Chicago and growing them under conditions that were 

 uniform and neutral to all of the complexes that were under examination. 

 Under experimental conditions of this sort the result will be an accurate measure 

 of the permanency of the character of the material in both its germinal and 

 somatic capacities to be reproduced in like values in successive generations. 

 (3) The analysis of the conditions of the population with pedigree analysis, 

 especially of the extreme conditions and of the most common condition. Collec- 

 tively the three will give answers to the problems investigated. 



EFFECTS OF TRANSPORTATION INTO A NEW HABITAT. 



In this method of testing the permanency of the array shown in a local popula- 

 tion, the results that have been obtained in transplanting materials from the 

 colonies at Chapultepec, Tlalnepantla, and Chalcicomula will serve to show the 



