Mr. Wallace goes on to quote further instances, such as that of Draba verna, which Jordan has found to present, in the south of France alone, no less than fifty-two permanent varieties, which all "come true from seed, and thus present all the characteristics of a true species"; so that, "as the plant is very common almost all over Europe, and ranges from North America to the Himalayas, the number of similar forms over this wide area would probably have to be reckoned by hundreds, if not by thousands[126]." [126] _Darwinism_, p. 77. One or two further quotations may be given to the same general effect, selected from the writings of specialists in their several departments. "There is nothing that divides systematists more than what constitutes a genus. Species that resemble each other more than other species, is perhaps the best definition that can be given. This is obviously an uncertain test, much depending on individual judgement and experience; but that, in the evolution of forms, such difficulties should arise in the limitation of genera and species was inevitable. What is a generic character in one may be only a specific character in another. As an illustration of the uncertain importance of characters, I may mention the weevil genus _Centrinus_ in which the leading characters in the classification of the family to which it belongs are so mixed that systematists have been content to keep the species together in a group that cannot be defined.... No advantage or disadvantage is attached, apparently, to any of the characters. There are about 200 species, all American. The venation of the wings of insects is another example of modifications without serving any special purpose. There is no vein in certain Thripidae, and only a rudiment or a single vein in Chalcididae. There are thousands of variations more or less marked, some of the same type with comparatively trivial variation, others presenting distinct types, even in the same family, such genera, for example, as _Polyneura_, _Tettigetra_, _Huechys_, &c. in the Cicadidae.