56 DOUBTFUL SPECIES. [Chap. II. 



describes a certain butterfly which presents in the 

 same island a great range of varieties connected by 

 intermediate links, and the extreme links of the chain 

 closely resemble the two forms of an allied dimorphic 

 species inhabiting another part of the Malay archipelago. 

 Thus also with ants, the several worker-castes are 

 generally quite distinct ; but in some cases, as we 

 shall hereafter see, the castes are connected together by 

 finely graduated varieties. So it is, as I have myself 

 observed, with some dimorphic plants. It certainly at 

 first appears a highly remarkable fact that the same 

 female butterfly should have the power of producing at 

 the same time three distinct female forms and a male ; 

 and that an hermaphrodite plant should produce from 

 the same seed-capsule three distinct hermaphrodite 

 forms, bearing three different kinds of females and 

 three or even six different kinds of males. Never- 

 theless these cases are only exaggerations of the 

 common fact that the female produces offspring of 

 two sexes which sometimes differ from each other in a 

 wonderful manner. 



Doubtful Species. 



The forms which possess in some considerable degree 

 the character of species, but which are so closely similar 

 to other forms, or are so closely linked to them by 

 intermediate gradations, that naturalists do not like to 

 rank them as distinct species, are in several respects the 

 most important for us. "We have every reason to 

 believe that many of these doubtful and closely allied 

 forms have permanently retained their characters for a 

 long time ; for as long, as far as we know, as have good 

 and true species. Practically, when a naturalist can 



