DEVELOPMENT OF THE IXODIDA, 15 
tially engorged nymphs usually have a much longer period of activity 
than fully engorged individuals. Low temperatures also lengthen 
this period. From 3 days to many months, varying somewhat 
with individuals, but particularly with the temperature, pass after 
the engorged nymphs drop before they transform to adults. 
THE ADULT. 
Upon molting, the adults may crawl upon herbage or other nearby 
objects and await a passing host. Some species, which commonly 
drop in places frequented by their hosts, may crawl about in search 
of them, as is the case with Rhipicephalus sanguineus. The lon- 
gevity periods are usually somewhat greater than those of the 
nymphs. In the case of those species which molt on the host, 
the female, after issuing from the exuvium, reattaches nearby, 
while the male detaches and goes in search of a mate. Copu- 
lation usually takes place upon the host, but with several species 
of Ixodes it occurs off the host as well. There are also several 
records of species of other genera where copulation occurred when 
the ticks were not on a host, but we are inclined to the opinion that, 
aside from ticks of the genus Ixodes, mating very rarely occurs off 
the host. The periods required by adults for engorgement are usually 
longer than those of the immature stages, as fertilization must, as a 
rule, first take place. We have found this period to vary consid- 
erably even in the same species. Fertilization appears to be one of 
the principal factors involved; the quantity and quality of the 
ingesta and the vitality of the individuals are also important factors. 
The rate of engorgement is greatly increased after the female has 
become about one-half engorged. Occasionally fully engorged 
females are unable to detach and remain attached for several days 
after becoming fully engorged. Our records show that females have 
engorged and dropped as soon as 5 days after attachment, while 
others have remained upon the host as long as 50 days. 
It has been found that females in the course of oviposition may 
first produce fertile eggs and later eggs which are dark, shrunken, and 
apparently infertile. Specimens of many of the species when not 
over one-third engorged may be detached and if uninjured will 
reattach. There is a great difference in the number of eggs deposited 
by the various species, varying with the size of the tick and also with 
the size of the eggs. This variation in the maximum number of eggs 
deposited ranges from 2,240 per tick in Hemaphysalis leporis-palustris 
to as many as 11,265 by our native species, Amblyomma maculatum, 
and 20,000 by 2 African species (A. hebreum and A. variegatum). The 
males often remain upon the hosts for long periods after the females 
have dropped; thus the females usually do not have to wait long for 
a mate after finding a host. The habit of the male of remaining upon 
