DOUBTFUL SPECIES 65 



to present 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 thus to differ in a slight degree. When the differ- 

 ences are rather more strongly marked, and when both 

 sexes and all ages are affected, the forms are ranked by all 

 entomologists as good species. But no observer can deter- 

 mine for another, 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, as varieties ; and those 

 which appear to have lost this power, as species. As the 

 differences depend on the insects having long fed on distinct 

 plants, it cannot be expected that intermediate links connect- 

 ing the several forms should now be found. The naturalist 

 thus loses his best guide in determining whether to rank 

 doubtful forms as varieties or species. This likewise neces- 

 sarily 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 in- 

 habits many islands in the same archipelago, and presents 

 different forms in the different areas, there is always a good 

 chance that intermediate forms will 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 the same identical 

 form is met with in two distinct countries, or in two geologi- 

 cal formations, they believe that two distinct species are hid- 

 den under the same dress. The term species thus comes to 

 be a mere useless abstraction, implying and assuming a sep- 

 arate act of creation. It is certain that many forms, consid- 

 ered by highly-competent judges to be varieties, resemble 

 species so completely in character, that they have been thus 

 ranked by other highly-competent judges. But to discuss 

 whether they ought to be called species or varieties, before 

 any definition of these terms has been generally accepted, is 



vainly to beat the air. 



c— lie XI 



