Origin of Different Kinds of Adaptations 351 



The differences between the castes have gone so far in 

 some of these groups that the majority of the members of the 

 community have even lost the power to reproduce their kind, 

 and this function has devolved upon the queen, whose sole 

 duty is to reproduce the different castes of which the com- 

 munity is composed. This specialization carries with it the 

 idea of the individuals being adapted to each other, so that, 

 taken all together, they form a whole, capable of maintaining 

 and reproducing itself. It does not seem that we must nec- 

 essarily look upon this union as the result of competition 

 leading to a death struggle between different colonies, so 

 that only those have survived in each generation that carried 

 the work of specialization one step farther. All that is re- 

 quired is to suppose that such specialization has appeared in 

 a group of forms living together, and the group has been able 

 to perpetuate itself. We do not find that all other members 

 of the two great groups to which the white ants and true ants 

 belong have been crowded out because these colonial forms 

 have been evolved. Neither need we suppose that during 

 the evolution of these colonial species there has been a death 

 struggle accompanying each stage in the evolution. If the 

 members of a colonial group began to give rise to different 

 forms through mutations, and if it happened that some of the 

 combinations formed in this way were capable of living to- 

 gether, and perpetuating the group, this is all that is required 

 for such a condition to persist. 



The relation of the parents to the offspring presents in 

 some groups a somewhat parallel case to that of these colonial 

 forms. Not only are some of the fundamental instincts of 

 the parents changed, but structures may be present in the 

 parents whose only use is in connection with the young. 

 The marsupial pouch of the kangaroo, in which the immature 

 young are carried and suckled, is a case in point, and the 

 mammary glands of the Mammalia furnish another illustration. 



Adaptations of these kinds are clearly connected with the 



