Origin of Species Variorum

has a few animals, now generally regarded as varieties, but which have been ranked as species by some zoologists. Several .. experienced ornithologists 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 Europe 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 can determine for others, even if he can do so for himself, ... which of these Phytophagic forms ought to be called species and which varieties. Mr. Walsh ranks the forms which it may be supposed would freely intercross together, as varieties; and those which appear to have lost this power, as