METAZOA INSECTA. 405 



As a ru'e among insects, whenever there is a decrease 

 in the size of the wings, it occurs in the female, while the 

 wings of the male are often remarkably large, but there 

 is a species among the Plecoptera, the Isogenus nubecula 

 (PI. 981, figs, i, 2), in which the wings of the female 

 (fig. i) are large, while those of the male (fig. 2) are 

 reduced to remnants. 



Order 5. PLATYPTERA. 



The termites possess certain Thysanuran characters in 

 the larval state, while in maturity they are developed 

 physiologically to a greater degree than any other mem- 

 bers of the generalized orders of insects. 



The larva of Termes (No. 982 ; PI. 983, fig. i, T. luci- 

 fitgus) has distinct thoracic and abdominal segments and 

 the two regions are broadly connected. It is white and 

 even the hooks of the feet are colorless, while the mandi- 

 bles are tinted only slightly. This condition indicates 

 that the larvae do little work, and this is the case, since 

 they are nursed and carefully tended when young and are 

 not obliged to shift for themselves. 



The pupae (No. 984; PI. 983, fig. 2) are essentially 

 like the larvae excepting in possessing wing pads. 



When, however, the adult forms are considered, we 

 find conditions wholly different from anything so far 

 described. The law of variation has acted, and speciali- 

 zation in function has produced modifications in structure. 

 At the same time the social instinct has developed to a 

 remarkable degree so that there appears, as a result, a 

 colony consisting of groups of many individuals, each 

 group having its special work to perform. 



If the course of development had been typical, that is 

 to say, if it had been similar to that of most insects, the 

 pupae would develop in every case into the male or 

 the female winged insect (No. 985, J ; No. 986, winged 



