CXXVl 



British Islands, that " their animal productions are so uniformly 

 identical with Continental specimens as to require no special 

 mention," only " some few British species differing slightly 

 from their continental allies." This opinion no longer holds 

 good, a rather large proportion of the resident species of these 

 islands being now known to differ in some way or another from 

 Continental or at least Central-European specimens. That 

 is not due to a change in the animals since Wallace's time, but 

 to a difference in the method of working on the part of the 

 systematist. As in everything, there are also two sides to 

 systematics : similarity and dissimilarity. If one of the two 

 sides is emphasised to the detriment of the other, a wrong 

 picture is presented of the actual state of things, and those 

 who rely for general conclusions on the work of the systematist 

 are bound to arrive at an erroneous conception of nature. 

 In Wallace's time the tendency was in the direction of appre- 

 ciating the similarity of the specimens from different countries 

 rather than the differences, which appeared superficial and 

 unimportant. For the Ornithologists of that time a Robin 

 from England, Germany or Madeira was a Robin ; they were 

 quite right inasmuch as these countries each have a Robin, 

 but were wrong in implying that these Robins were identical. 

 And that applies equally to a multitude of other species in all 

 orders of animals. We now speak of Scotch forms of 

 Lepidoptera, of British and Irish forms, and it is common 

 knowledge among British Lepidopterists that in a number of 

 instances the species are not identical even in different districts 

 of England. The Oak-egger from the shingle beach of Sheer- 

 ness is very different from the form found inland; the 

 Ruby Tiger {Phragmatobia fuliginosa) from the mountains of 

 Scotland is very distinct from more southern specimens; 

 Coenonyvipha davus from Scotland and Northern England are 

 by no means alike ; and Mclitaea artemis from Kent, Cornwall 

 and Ireland show considerable differences. The Irish Satyrus 

 scmele and Spilosoma mendica contrast strongly with British 

 specimens ; and the Hepialus humuli from the Shetlands in 

 which the sexes are praccically alike in markings, while in other 

 countries the species is sexually dimorphic, is one of the well- 

 known classical examples of geographical variation. 



