METAZOA INSECTA. 487 



which fit the laborers for their special duties. Not only 

 are there males (PI. 1245, fig. i, Formica pennsylvanica 

 De Geer), females (fig. 2), and workers (fig. 3), as in the 

 bee, but there are soldiers (fig. 4) and the workers and 

 soldiers are differentiated still further so that other forms 

 appear, each one with its particular work to perform. 



The males and females are provided with wings until 

 after the nuptial flight, when the males are killed and the 

 female sheds these organs. The workers, however, are 

 always wingless, and are therefore examples of specializa- 

 tion by reduction. Even the sutures between the seg- 

 ments on the dorsal side are often obliterated, while they 

 may be clearly seen in the winged male and female. 



A colony of ants consists of males, many queens instead 

 of one as in the bees, and thousands of workers and sol- 

 diers. The workers do all the industrial work of the nest, 

 while the soldiers with their great heads and strong man- 

 dibles defend the colony. The winged individuals and 

 the workers and soldiers of some species, Atta for instance 

 (No. 1246, A. fervens Say, $ ; No. 1247, the same, $) 

 are differentiated so that the subject of polymorphism is 

 admirably illustrated. 



The organization of the colony continues for years and 

 the mother ant lives to see her children grow to maturity. 

 It seems that the young are more helpless and also more 

 tenderly cared for than in any other group of insects. 

 They have the advantage of living with the old ants and 

 of profiting by their experience. These conditions exist- 

 ing for unnumbered years and countless generations have 

 led to the present efficient and intelligent social order. 



Order 16. DIPTERA. 



The Diptera illustrate pre-eminently the efficiency 

 which may be attained through specialization by reduc- 

 tion. These specializations will be brought out more 

 clearly when considering a typical form of the order, 



