THE RABBIT DERMACENTOR. 159 
excrete large amounts of what appears to be undigested blood, 
while engorging. 
THE RABBIT DERMACENTOR. 
Dermacentor parumapertus marginatus Banks. 
The common name of this tick is taken from the fact that in the 
adult stage it is found on no other host than the rabbit, while the 
adults of other species of the genus Dermacentor are very rarely 
found on that host. 
DESCRIPTIVE. 
Adult (Pl. XIII, figs. 3-5).—Males from 2.5 by 1.25 mm. to 3 by 
1.75 mm. Females, unengorged, 2.5 by 1.5 mm. to 3.75 by 2 mm.; 
engorged, 10 by 7 by 3.5 mm. to 15.4 by 10.7 by 7.7mm. The males 
have interrupted white markings along the lateral borders of the 
dorsum. The posterior border of the scutum of the females is white, 
the lateral borders with interrupted white markings. In both sexes 
the outer surface at the apex of the leg segments is marked with white, 
in which are usually two dark red punctations. Some specimens from 
California, Oregon, and Utah have no white visible, while others 
are nearly as strongly marked as those from New Mexico and Texas. 
Nymph (Pl. XIU, fig. 2)—Unengorged, about 1.23 by 0.79 mm.; 
engorged, 3 by 2.1 by 1.2 mm. to 3.9 by 2.8 by 1.6 mm. Color, 
unengorged, reddish brown; engorged, dark slate to almost black. 
Capitulum 0.305 mm. long (from tip of palpi to base of emargination 
of scutum); scutum 0.524 mm. long by 0.521 mm. wide. 
Larva (Pl. XIII, fig. 1)—Unengorged, about 0.686 by 0.433 mm. 
(alcoholic) ; engorged, 1.3 by 0.8 by 0.7 mm. to 1.5 by 0.9 by 0.8 mm. 
Color, unengorged, reddish yellow; engorged, dark slate. Capitulum 
0.148 mm. long (from tip of palpi to base of emargination of scutum); 
scutum 0.260 mm. long by 0.344 mm. wide. 
Egg.—Ellipsoidal, yellowish brown, shining, smooth. The average 
size of 10 measured was 0.65 by 0.47 mm. 
HOST RELATIONSHIP. 
The host of the type variety is the jack rabbit. The types of the 
species (D. parumapertus) are labeled as taken from man and in a 
chicken house. Nospecimens of this variety have been taken on other 
hosts than jack rabbit and cottontail rabbit. While very few larve 
and nymphs have been collected on rabbits, it would appear from 
the fact that no specimens have been taken on any other animal 
that the rabbit is the principal host of those stages. We have en- 
gorged larve in our rearing experiments on the fox squirrel, guinea 
pig, and bovine, as well as rabbit, and nymphs have been engorged 
on the guinea pig and rabbit. 
Although a large number of unengorged adults have been col- 
lected, very few fully engorged females have been obtained. It would 
seem that a large number of them are scratched off by the host before 
becoming replete. The species is found principally in the ears of 
