ASPECTS OF KINETIC EVOLUTION 347 



ferent directions, so that more than a dozen different and dis- 

 tinct types of individuals may be found in the same colony, 

 and no intermediate forms. 



The equal sharing of the two sexes in these wonderful 

 specializations of the termites is a reminder of the general fact 

 of numerical equality between the sexes. Among the bees 

 where the male sex is completely useless in the social economy 

 and environmental relations of the colony, the reduction of the 

 number of males has been accomplished only by the very re- 

 markable specialization of the reproductive process. The sex 

 is no longer determined by a polarity or other simple relation 

 which would give equality of sexes, but by the queen herself, 

 who has the power of laying at will either fertilized or unferti- 

 lized eggs, the former developing into females, the latter into 

 males. This arrangement appears peculiar because it consti- 

 tutes so radical an exception to the general rule of equality in 

 the choice by individuals of one or the other of the two routes 

 of development possible in all sexually differentiated species. 

 If these relations depended upon merely mechanical arrange- 

 ments or upon the relative numbers of different kinds of pure 

 germ-cells, we should expect the frequent occurrence of many 

 definite deviations from equality of sexes. 



Experiments have shown that in some groups of animals and 

 even in plants the sex-determination may be influenced by the 

 conditions of existence, and particularly by nutrition and tem- 

 perature. The changes are supposed, however, to occur in 

 continuous series of gradations, as though brought about by 

 general influences upon the constitution of the organism, rather 

 than by the abrupt changes of adjustment which might be ex- 

 pected to result from the action of character-unit devices. 



The phenomena of Mendelism constitute an extension of the 

 facts of alternative descent ; for they show that this is not limited 

 merely to secondary sexual characters and to the form differ- 

 ences of polymorphic species, but that closely similar effects 

 can be obtained in a somewhat artificial manner, by com- 

 bining domesticated varieties with properly opposed characters. 

 Instead of producing merely averages or miscellaneous grada- 

 tions of intermediates, well established and contrasted differ- 



