emerging from the egg
is very minute, six-legged, and is just visible to the naked eye. (Pl.
XLVI, fig. 3.) If these larvae are kept on a layer of moist sand or earth in
a covered dish, they may remain alive for months, but there is no
appreciable increase in size. So soon, however, as they are placed upon
cattle growth begins.

On pastures these little creatures soon find their way on to cattle. They
attach themselves by preference to the tender skin on the escutcheon, the
inside of the thighs, and on the base of the udder. Yet when they are very
numerous they may be found in small numbers on various parts of the body,
such as the neck, the chest, and the ears. (Pl. XLVIII and Pl. XLIX, fig.
1.)

The changes which they undergo during their parasitic existence were first
studied by Dr. Cooper Curtice, of the Bureau of Animal Industry, in 1889.
The young tick molts within a week, and the second or nymphal stage of the
parasite's life is thus ushered in. After this change it has four pairs of
legs. Within another week another molt takes place by which the tick passes
from the nymphal to the sexual, or adult, stage. Impregnation now takes
place, and, with the development of the ova in the body, the tick takes an
increased quantity of blood, so that in a few days it becomes very much
larger. That the rapid growth is due to the blood taken in may be easily
proved by crushing one. The intestine is distended with a thick, tarry mass
composed of partly digested blood. When the female has reached a certain
stage of maturity she drops to the ground and begins to lay a large number
of eggs, which hatch in the time given above.

The life of the cattle tick is thus spent largely on cattle, and although
the young, or larvae may live for a long time on the ground in the summer
season, they can not mature except as parasites on cattle and horses. We
have purposely omitted various details of the life history, including that
of the male, as they are not necessary to an understanding of our present
subject--Texas fever. How this is transmitted we will proceed to consider.
Before the enforcement of the Federal quarantine southern cattle sent north
during the spring and summer months carried on their bodies large numbers
of the cattle ticks, which, when matured, would drop off and lay their eggs
in the northern pastures. After hatching, the young ticks would soon get
upon any northern cattle which happened to be on the pasture. So soon as