260 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 
TIME OF BIRTH AND NUMBER OF YOUNG. 
The time of reproduction varies with the latitude and altitude, but 
exact information as to the dates of birth and the number of young- in 
a litter in different parts of the plains is not at hand. In Texas the 
young are usually seen at the mouths of the holes in early May, while 
in North Dakota and Montana they rarely appear before the latter 
part of May or first week of eJune. The usual number of j^oung 
seems to be four, but the cases in which the number is definitely 
known are few. 
MOUNDS AND BURROWS. 
The mouth of each burrow opens in the middle of a mound, which 
is usually a foot high and 3 or 4 feet in diameter (PI. XXIII, lig. 1). 
The mound increases in size with age, those that have been used for 
many years attaining a height of li or 2 feet and a diameter of 8 or 
10 feet. The interior of the mound is funnel-shaped, forming an 
elevated crater-like rim around the entrance of the hole. This is 
pressed into form by the nose of the animal, as may be seen in PL 
XXIII, fig. 3, which shows prints of the nose all around the inside. 
After injury from rains or other causes the rim is repaired by scrap- 
ing up the ground from outside (PI. XXIII, fig. 2). Sometimes the 
repairs are made before rains, and some observers regard the animals 
as exceptionally clever weather prophets. Thus, Maj. H. W. Merrill 
states that whenever they are busy scraping the earth up around their 
burrows and pressing it into place with their noses rain is sure to 
follow in a very short time. The chief object of the elevated rim is 
to keep the water out of the burrows when the ground is flooded by 
sudden rains, as shown in PI. XXIV, fig. 1. The ground immediately 
surrounding each burrow is usually cleared of small plants and kept 
clean and bare, and where burrows are near together the bare areas 
often join, so that in thickly populated colonies the ground is hard 
and smooth like a playground, and the animals are obliged to go some 
distance for food. This the}^ dislike to do, lest they be pounced upon 
by enemies; hence, when the grass near their burrows has been con- 
sumed they dig new holes nearer the suppl3\ It takes a long time 
for vegetation to regain a foothold on the hard floors of the dog 
towns, and the sites of old towns remain conspicuous for years after 
they are abandoned. 
The holes go down for some distance at a very steep angle and then 
turn at nearly a right angle and continue horizontally, rising some- 
what toward the end. The nests are in side chambers connecting 
w^ith the horizontal part of the burrow, and usually, if not always, 
at a somewhat higher level (fig. 25, //). Recently, at Alma, Nebr.. 
W. H. Osgood dug out a burrow, of which he made a careful 
diagram (fig. 25), accompanied by measurements. In this case the 
