276 CONCLUDIDG KEMAEKS Chap. VE 



of these cases is there any reason to believe that the 

 several males or several females of the same species 

 differ in their sexual powers, except in the atrophied 

 condition of the reproductive organs in the workers 

 of social insects. Many hermaphrodite animals must 

 unite for reproduction, but the necessity of such 

 union apparently depends solely on their structure. 

 On the other hand, with heterostyled dimorphic 

 species there are two females and two sets of males, 

 and with trimorphic species three females and three 

 sets of males, which differ essentially in their sexual 

 powers. We shall, perhaps, best perceive the complex 

 and extraordinary nature of the marriage arrangements 

 of a trimorphic plant by the following illustration. 

 Let us suppose that the individuals of {he same species 

 of ant always lived in triple communities; and that 

 in one of these, a large-sized female (differing also in 

 other characters), lived with six middle-sized and six 

 small-sized males; in the second community a middle- 

 sized female lived with six large- and six small-sized 

 males; and in the third, a small-sized female lived 

 with six large- and six middle-sized males. Each of 

 these three females, though enabled to unite with any 

 male, would be nearly sterile with her own two sets of 

 males, and likewise with two other sets of males of the 

 same size with her own which lived in the other two 

 communities; but she would be fully fertile when 

 paired with a male of her own size. Hence the thirty- 

 six males, distributed by half-dozens in the three com- 

 munities, would be divided into three sets of a dozen 

 each; and these sets, as well as the three females, 

 would differ from one another in their reproductive 

 powers in exactly the same manner as do the distinct 

 species of the same genus. But it is a still more 

 remarkable fact that young ants raised from any ona 



