( xxxiv ) 



consi)icHOiis or scarcely perceptible ; the gap between two geograjihically separate 

 entities may be small, or large, and it may be completely bridged over by 

 individuals from other countries. A careful observer of any group of sexually 

 separate animals will know ■ many instances referable to the various cases 

 alluded to. We will call such geographically sejiarate animals which are 

 different, qeoiivnithical representatires. 



In order to see clearly what the difference means, it is necessary to 

 know the meaning of identity in geographically sejiarate individuals. If two 

 geographically separated specimens prove on comjjarison to be identical, or are 

 considered identical, the student has to conclude that they are not separated by 

 tiiat barrier which we have above characterised as effectively keeping the entities 

 of the same country (= synoecic entities) apart. As each of the two individuals 

 is a portion of an entity in its native country, these two respective entities 

 are also not separated by that barrier. That means, the two entities together 

 are only one single entity separated from all the others by the above barrier. 

 We cannot help adding, that it appears very strange to us to see some indi- 

 viduals pronounced identical, and to iind them, nevertheless, treated by the same 

 author as belonging to two " species." * 



It is clear, from what we have just said, that geographically separate 

 animals which are identical in some of the individuals, or, in other words, of 

 which the range of variation overlaps (A' varying from 1 to 5, A- from 4 to 

 12, A' from 7 to 19, A^ from 18 to 21, etc.), are one biological entity; that 

 is to say, the geographically separate different specimens are the product of 

 geographical variation of the same animal. 



It is a difficult task to find out the limits of variation. The material 

 which comes into the hands of the student being insignificant compared with 

 the number of individuals at large, it depends upon chance that the extreme 

 individuals become known. Ex[)eriments, es])ecially with Lepidoptera, have 

 proved that the range of variation can be increased artificially. That is to say, 

 the capability to vary is greater than we generally observe it to be in the 

 material collected, and therefore we must expect that the range of variation is 

 in many cases actually more extended than we see it, and that, consequently, 

 very often also those geograjihically separated different animals overlap in 

 characters which differ constantly in the specimens contained in collections. If 

 the number of individuals is small (we know frequently only one or a few 

 specimens, often only one sex), it is the merest assumption to say that all the 

 specimens of the respective locality are difterent from all the individuals of a 

 certain other locality. And an author who makes such a statement is no less 

 h'asty or superficial in his judgment than the one who waves the distinctions 

 aside as being of no importance. However, if there is any reason for expecting 

 the characters to overlap, it follows from what we said before, that the 

 individuals from the two places together belong to one entity. The accom- 

 panying diagram (Fig. 1) demonstrates ])erhaps more clearly the correctness of 



* See \o)\ Zool IX. p. 459 4(J3 (1902). 



