Origin of Species Variorum

Comparison with 1872

consider our British red grouse as only a strongly-marked race of a Norwegian species, whereas the greater number rank it as an undoubted species peculiar to Great Britain. A wide distance between the homes of two doubtful forms leads many naturalists to rank them as distinct species; but what distance, it has been well asked, will suffice; if that between America and Europe is ample, will that between the Continent and the Azores, or Madeira, or the Canaries, or between the several islets of these small archipelagos, be sufficient? ↑

Mr. B. D. Walsh, a distinguished entomologist of the United States, has lately described what he calls Phytophagic varieties and Phytophagic species. Most vegetable-feeding insects live on one kind of plant or on one group of plants; .. some feed indiscriminately on many .. kinds, ↑ but do not in consequence vary. In several cases, however, insects found living on different plants have been observed by Mr. Walsh to present, either exclusively in their larval or mature state, or in both states, slight, though constant differences in colour, size, or in the nature of their secretions. In some instances the males alone, in other instances both males and females, have been observed to be thus affected in a slight degree. When the differences are rather more strongly marked, and when both sexes and all ages are affected, the forms would be ranked by all entomologists as species. But no observer

consider our British red grouse as only a strongly-marked race of a Norwegian species, whereas the greater number rank it as an undoubted species peculiar to Great Britain. A wide distance between the homes of two doubtful forms leads many naturalists to rank both as distinct species; but what distance, it has been well asked, will suffice? If that between America and Europe is ample, will that between Europe and the Azores, or Madeira, or the Canaries, or between the several islets in each of these small archipelagos, be sufficient? ↑

Mr. B. D. Walsh, a distinguished entomologist of the United States, has lately called attention to some cases, analogous with those of local forms and geographical races, yet very different from them. These cases he has fully described under the terms of Phytophagic varieties and Phytophagic species. Most vegetable-feeding insects live on one kind of plant or on one group of plants; but some feed indiscriminately on many widely distinct kinds, yet this induces no change in them. Mr. Walsh, however, has observed other cases in which either the larva or mature insect, or both states, are thus affected by slight, though constant, differences in colour, or size, or nature of their secretions. In one case difference in food was accompanied by several slight but constant structural differences in the mature male alone. In other cases both males and females are thus slightly affected. Lastly, differences of food apparently cause more marked and constant differences in colour or structure, or in both combined, in the larva and in the mature insect. Forms modified to this degree are ranked by all entomologists as distinct, though allied, species of the same genus. The slighter differences, as in colour alone, and confined to the larva alone, to the mature insect alone, are almost invariably looked at as mere varieties. But no man