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 
