328 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
In the region about the headwaters of the Paraguay the nests of the 
white ants are extremely abundant in favorable localities, and the 
forms of the nests are different from those noted in other parts of trop- 
ical America. The tall and very slender forms are especially notice- 
able in the low, flat prairie lands south of Cuiaba. (See fig.8.) These 
slender forms are known in that part of Brazil by the Indian name of 
tacurt. 
Age of the mounds.—The method of building the mounds and the 
habits of the termites, so far as J am acquainted with them, lead to the 
conclusion that the size of a mound is determined by its age and by the 
size of the colony building it. Just how long it requires to build the 
large mounds I have but little means of judging. One frequently sees 
nests built on houses and fences, and in these cases it has been possible 
to determine the maximum ages of these particular nests. These 
peers 
he ee. 
Fig. 8.—White ants’ nest of earth in Matto Grosso, on the plains of the Upper Paraguay. 
{Sketch by J. C. Branner.]} 
cases, however, afford only a suggestion. The oldest nests I have 
seen, and of which I could get an idea of their ages, were not more 
than 50 years old, and the biggest of them contained a little less than 
1 cubic meter of earth, the estimate being made without reference to 
the cavities within the mass. 
It is evident that the size and age in one of these cases may or may 
not help one to determine the time occupied in the construction of one 
of the very large nests figured in this paper, for the rates of building 
may have been very different. 
UNDERGROUND STRUCTURES. 
The above-ground structures of the white ants connect with under- 
ground passageways, but wherever I have seen these passageways 
opened they appeared to have been excavated and then to have been 
