VARIATION UNDER NATURE 79 



treme 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 cer- 

 tainly 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 a 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. Nevertheless 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 constderable degree 

 the character of species, but which are so closely similar 

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

 mediate 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 unite by means 

 of intermediate links any two forms, he treats the one as 

 a variety of the other; ranking the most common, but 

 sometimes the one first described, as the species, and the 



