56 DOUBTFUL SPECIES. [Chap, rf, 



butterfly which presents in the same island a goeat 

 range of varieties connected by intermediate links,/ and 

 the extreme links of the chain closely resemble thf3 two 

 forms of an allied dimorphic species inhabiting an- 

 other part of the Malay archipelago. Thus also with 

 ants, the several worker-castes are generally/ quite 

 distinct; but in some cases, as we shall hereafjter see, 

 the castes are connected together by finely graiduated 

 varieties. So it is, as I have myself observed, with some 

 dimorphic plants. It certainly at first appears Sft highly 

 remarkable fact that the same female butterfly 

 should have the power of producing at ^the same 

 time three distinct female forms and a malej and that 

 an hermaphrodite plant should produce from; the same 

 seed-capsule three distinct hermaphrodite fo;rms, bear- 

 ing three diflEerent kinds of females and three or even 

 six different kinds of males. Nevertheless these' 

 cases are only exaggerations of the comf^mon far/^t 

 that the female produces offspring of two sesi^s 

 which sometimes differ from each other in a wonder.tf^l 

 manner. 



Doubtful Species. 



The forms which possess in some considertible de/?ree 

 the character of species, but which are so closely siipil^r 

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

 mediate gradations, that naturalists do not lii^e to 

 rank them as distinct species, are in several respect-* i-he 

 most important for us. We have every reason to be- 

 lieve that many of these doubtful and closely allied 

 forms have permanently retained their character^ for a 

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

 and true species. Practically, when a naturalist pan 



