5G DOUBTFUL SPECIES. CnAP. II, 



Malay archipelago. Tlius also with ants, the several worker- 

 castes are generally cjuite distinct ; but in some cases, as we 

 shall hereafter see, the castes are connected together by gradu- 

 ated varieties. It certainly at first appears a highly-remark- 

 able fact that the same female butterfly should have the power 

 of producing at the same time three distinct female forms and 

 a male ; that a male Crustacean should generate two male 

 forms and a female form, all widely different from each other ; 

 and that an hermaphrodite plant should produce from the same 

 seed-capsule three distinct hermaplu-odite forms, bearing three 

 different kinds of females and three or even six different kinds 

 of males. Nevertheless these cases are only exaggerations of 

 the universal fact that every female produces males and females, 

 Avhich in some instances differ in a wonderful manner fj-omeach 

 other. 



Doubtful jSpecies. 



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 grada- 

 tions, 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 

 in their own country for a long time ; for as long, as far as we 

 knoAV, as have good and true species. Practically, when a 

 naturalist can unite two forms together by othei*s having inter- 

 mediate characters, he treats the one as a variety of the other, 

 ranking the most common, but sometimes the one first de- 

 scribed, as the species, and the other as the variety. But 

 cases of great difliculty, which I will not here enumerate, 

 sometimes occur in deciding whether or not to rank one form 

 as a variety of another, even when they are closely connected 

 by intermediate links ; nor will the commonly-assumed hybrid 

 nature of the intermediate links always remove the difficulty. 

 In very many cases, however, one form is ranked as a variety 

 of another, not because the intermediate links have actually 

 been found, but because analogy leads the observer to suppose 

 either that they do now somewhere exist, or may formerly 

 have existed ; and here a wide door for tlie entry of doubt and 

 conjecture is opened. 



Hence, in determining whether a form should be ranked as 

 a species or a variety, the opinion of naturalists having sound 



