THE RABBIT DERMACENTOR. 163 
The nymph (Table LXXIV).—The greatest longevity of nymphs 
observed by us was 175 days. This record was made on a lot of 7 
nymphs which molted from larvae October 27-31, 1910, and were . 
kept on moist sand in the laboratory. In another lot of 22 nymphs 
which molted from larvee October 27 to November 5, 1909, 2 were 
alive March 9, 1910, when they were put on a host, thus having lived 
at least 144 days. Three lots of unengorged or slightly engorged 
nymphs collected on rabbits lived from 30 to 100 days. 
Attempts to get nymphs to attach to a bovine failed and in our 
early experiments no attachments were secured when the nymphs 
were put on tame rabbits and guinea pigs. In 1910, two attempts to 
attach nymphs to a fox squirrel failed, and similar results were 
experienced in two of six tests on guinea pigs. In one instance a 
single nymph attached readily to a guinea pig, and 2 nymphs put on a 
rabbit attached and engorged readily. 
The shortest period of engorgement observed was 4 days and the 
longest 25 days. 
TaBLE LXXIV.—Engorgement of nymphs of Dermacentor parumapertus marginatus. 
Nymphs dropped engorged—days following 
N application. Toial 
Date nymphs applied. Host. vets number 
dropped. 
Dees 10) 1909 maces y ae Guinea pig... 9 0 1 0 1 1 1 0 4 
HeDaaLOLO Rosse. Sree SA a dol2e32 1 0 0 0 0 0 0 1 1 
Mar 25 G1 0o2 Fela hassctee Rabbit...... 2 1 0 1 0 0 0 0 2 
Nymphs which dropped in August molted in 21 days when the 
mean temperature was 88.25° F, One nymph which dropped Decem- 
ber 19, 1909, molted 123 days later. This was the longest molting 
period observed. During this period the mean temperature was 
60.24° F. The mean temperature has a decided effect on the length 
of the molting period. The molting periods of those nymphs which 
become males and those which become females are about the same. 
A total effective temperature of 641° F. appears to be required to pro- 
duce this molt. 
The adult (Table LXXV).—The number of individuals of each sex 
was practically the same in the adults which we observed to molt from 
nymphs. The greatest longevity recorded occurred in a lot of 11 
males and 4 females which were collected on rabbits on April 21-25, 
1910. On August 18, 1910, a male and a female were alive, but these 
died before September 26, 1910, having lived between 115 and 158 
days. Of a lot containing 21 males and 8 females which molted 
between May 12 and May 30, 1910, 2 males and 2 females lived 
between 80 and 137 days. A number of other lots of collected indi- 
viduals lived from 25 to 72 days. The longevity of the sexes is prac- 
tically the same. 
Unengorged or slightly engorged males and females taken from 
rabbits have readily attached when placed upon a bovine host. 
