Chap. II. DOUBTFUL SPECIES. 59 



rather more strongly marked, and when both sexes and all aj^os 

 are afTectcd, the forms -would be ranked by all entomolo<^ists 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 Avhich appear to have lost this jjower, 

 as species. As the ditfcrences depend on the insects having 

 long fed on distinct plants, it cannot be expected that inter- 

 mediate links connecting tlie several forms should now be 

 found. The naturalist thus loses his best guide in determining 

 whether to rank such doubtful forms as varieties or sjiecies. 

 This likewise necessarily occurs with closely-allied organisms, 

 which inhabit distinct continents or islands. When, on the 

 other hand, 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 good 

 chance that intermediate forms may be discovered which shall 

 link together the extreme states ; and these arc then degraded 

 to the rank of varieties. 



Some few naturalists maintain that animals never present 

 varieties ; but then these same; naturalists rank the slightest 

 differences as of specific value; and when the same identical 

 form is met with in two distant countries, or in tM'o geological 

 formations, they believe that two distinct species are hidden 

 under the same dress. Tlie term species thus comes to be a 

 mere useless mental abstraction, implying and assuming a sepa 

 rate act of creation. It is certain that many forms, considered 

 by highly-competent judges as varieties, so completely resemble 

 species in character, that they have been thus ranked by other 

 highly-competent judges. But to discuss whether they ought 

 to lie called species or varieties, before any definition of these 

 terms has been generally accepted, is A'ainly to beat the air. 



Many of the cases of strongly-marked varieties or doul)tful 

 species well deserve consideration ; for several interesting lines 

 of argument, from geographical distribution, analogical varia- 

 tion, hybridism, etc., have been brought to l)ear on tlie attempt 

 to determine their rank ; but space does not here permit me 

 to discuss them. Close investigation, in many cases, will bring 

 naturalists to an agreement how to rank doubtfid forms. Yet 

 it must be confessed that it is in the best-known countries that 

 we find the greatest number of forms of doubtful value. I 

 have been struck Avith the fact that, if any animal or plant in a 



