158 Biology of Dermacentor 
The nymphal tick escaped by crawling forward and to one side after 
the larval skin had been ruptured. The skin split from a point posterior 
to the hind coxae along the margins of the tick slightly above the coxae, 
then the break turned dorsally at the anterior end so as to reach the 
scutum near the eyes. From these points the fissures extended 
posteriorly along the margin of the scutum to its tip where the two 
ruptures met. The exuvium was left firmly attached by the tarsal 
claws. The abdominal portion was almost white and the highly 
chitinised portions changed little in colour compared to those of the 
larva. 
The Nymph: Little has been learned regarding the habits of the 
nymph, as only one nymph has been observed. This individual 
moulted from the larval stage on April 19, 1911. On May 12, 1911, it 
was placed on a guinea-pig. It became attached readily and five days 
later was noticeably larger. At this time a number of small pellets of 
excrement were observed in the hair beneath the tick. On May 18 the 
nymph was J to \ engorged and the abdomen had taken on a dark 
bluish-gray colour. The subsequent evening at 7 o’clock it appeared to 
be fully engorged. On the morning of May 20 it was found to have 
dropped from the host, having had an engorgement period of To¬ 
days. The measurements of this individual were : 4'9 mm. in length 
(including capitulum), 2'7 mm. in width, and 1'6 mm. in thickness. 
The body was slate coloured; the scutum reddish-brown anteriorly, 
darker at tip; and the legs, coxae and capitulum, light reddish-brown. 
This nymph transformed to a male on June 12, 1911, or 23 days 
after dropping off the host. During this period the mean temperature 
was 86‘5° F. 
In moulting the nymphal skin ruptured immediately above the 
stigmal plates on either side. These splits extended posteriorly along 
the ventral ends of the festoon grooves, and met at the posterior end. 
They also extended anteriorly and dorsally until opposite the first coxae, 
when the rupture ran dorsally on either side to a point on the scutum 
near the eyes. The tick then escaped through the posterior end of the 
skin. As the tick escaped two ruptures ran dorsally from the primary 
fissure along the first festoonal grooves on either side. These extended 
up to the marginal groove and the portion of the integument bearing 
the festoons was raised up, bending hinge-like along the marginal 
groove. This process of moulting, as well as that observed in the larva, 
is practically identical with that which we have observed to occur in 
other Dermacentors which moult off the host. 
