Origin of Species Variorum

can draw the line for others, even if he can do so for himself, and determine with certainly which of the several phytophagic forms to call varieties and which to call species. Mr. Walsh, who argues with much force that the different states have gradually passed into each other, is forced to assume that those forms, which it may be supposed would freely intercross, should be designated as varieties, whilst those which have probably lost this capacity for intercrossing should be called species. ↑ As the difference in all these cases clearly depends on the insects having long fed on perfectly distinct plants, intermediate links between the several forms thus produced cannot be expected to be found; though formerly such must have existed, connecting the present divergent forms with their common progenitor. The naturalist thus loses his best guide in determining whether to rank such doubtful forms as varieties or species. This likewise necessarily occurs with closely allied organisms, of doubtful value, which inhabit separate continents or distant islands. But when an animal or plant ranges over the same continent or inhabits many islands in the same archipelago, and presents different forms in the different areas, there is always a chance, which is not rarely successful, that intermediate forms may be discovered which will link together the extreme states; and these are then degraded to the rank of varieties.

Some few naturalists maintain that animals never present varieties; but then these same naturalists rank the slightest difference as of specific value; and when even the identically same form is met with in two distant countries, or in two distinct geological formations, they go so far as to believe that two separate species are hidden under the same dress. The term species thus comes to be a mere useless mental abstraction, implying