146 HAROLD HEATH AND BLAKE C. WILBUR. 



fore be considered to indicate with a fair degree of accuracy the 

 rate of increase from year to year. In 19 nests, examined in July 

 and August (the months when colonies normally are established), 

 the number of individuals, not including unhatched embryos, 

 varied from 2 to 17. These probably belonged to communities 

 not more than one year of age. In 16 other associations the num- 

 ber ranged from 31 to 47. Since these were collected during the 

 late summer, and no intermediate numbers connected them, it is 

 reasonable to conclude that these larger colonies were two years 

 old. In ii cases the membership ranged from 97 to 121 ; these, it 

 is believed, are three years of age. Finally there were 14 colonies 

 numbering 327 as a minimum and 497 as a maximum probably a 

 four-year development. 



Whether these figures are strictly correct or not, it is certain 

 that in the early years of colony development the rate of increase 

 in the number of offspring of Tcrmopsis is comparatively slow. 

 Even in old colonies, where the royal pair is surrounded by a 

 thousand or more descendants, the egg tubes never become so 

 numerous that they reduce the queen to an inert reproductive sac 

 as in the case of certain tropical species. Hence it is safe to as- 

 sume, on the basis of extended observations, that a community 

 with 450 members is certainly three years of age if not four as 

 the above figures indicate. 



As previously mentioned, no individual with wing buds has been 

 discovered in young colonies. To be more explicit none are 

 known to appear before the members of a community total ap- 

 proximately 450. In the case of T. nevadensis, for example, 

 there were two nymphs of this type in a colony numbering 454 

 individuals, 6 were in another colony of 467 members, 7 in one 

 with 497 and 39 in one with a total of 490. Beyond this point the 

 number of winged individuals mounts fairly rapidly until in old 

 colonies, judging from the extent of the burrows as well as the 

 size of the population, they may outnumber those of the soldier 

 caste. In the case of T. angusticolis the same feature exists, but 

 from data in hand the winged individuals put in an appearance at 

 a somewhat later date when the number of inhabitants is nearer 

 500. 



Before entering upon a detailed description of the development 



