THE ROCKY MOUNTAIN SPOTTED-FEVER TICK. 173 
drop fully engorged on the third day after application. The longest 
period required for engorgement, of these reattached nymphs, was 6 
days. 
TaBLE LXXIX.—Engorgement of nymphs of Dermacentor venustus. 
Total 
Date nymphs applied. Host. Slee sh eS, number 
; dropped 
3 1 5 6 7 8 
¢ —<—<——  s§- ——————— 
1908. 
i ATOSIYS 3 a le rele lip dR bac eae Bovinesss-2-- Oa cscs 2 17 13 2) eractr eel eece 34 
Cy Se ee are a ee eee Opec TB ylee-. 2 6 3 4 | ees ee 16 
1909. 
AAU SSC TS cS ie ae Rabbiteso-2-- 10 1 5 Balt nes: as Beet i eer | ale at 9 
INE Sn ee eres Guinea pig.... CB ct cic 1 10) Se eee ee © ome See | ae ee 2 
NeptnOrey eee o.ee ntae Rabbit... 22... | ule hee 2 Lr | cee le eee See) 7 
Onli) ; Seen eens ae Bovine ae Tal 9g 4| Reno lard sk HP aeeee Dy ee ae 3 
1910. 
MANUS. Sa tice sete es one Goings pies! TOES | oie. sacs: 2 1 al ee ea a 5 
EATON AU ee ee | Squirrel....... LOA OA sales Be 2 Saleh sce eee oa ee 7 
LN TE gl Ls ee Sa Sane aa | Guinea pig... . Sh ore et | Se al (eo alg | Sa QW bee) Saves 1 3 
RY, CE a eee 2 |) BOWING. <2 .))-% Silos dle rgse ve secrete Alec ae sle tones is. ag. 4 
STEUER 2% ae ba cn 4 ea eo aaa | Rabbit..3--5-- TOE cme emcees 7 Ini\Geee sel ngeee |B a3e- 8 
INTERAC Ua Se See. Bie Semen Nee dDAste2eA: ee eee 5 Bt Saal eee: [Sees | ae 8g 
ENGR A os eee Baca dowrnes: iG) eens || Seapets 8 2 ele certs | eae 1 
Aug s Tet: 2 2 Bee Ree Guinea pig. ..- 30 7 12 Silkcesseleeeia-ole setee| =a eeec 22 
PROTO ne meets cic sin oie ss RabDitess-.-- 4a eee 5 nh eee ee SS se eee 1 7 
DACRE oe oe ge ee Oe Guinea pig.... Os lese a. pees 4 21g eae one eer SS bee 8 
Total ..%. 25) cl ee eae iit ec Ie Oreo) tases tel et eee 154 
A aie individuals were collected on hosts when unengorged or slightly engorged and reattached on this 
In our observations engorged nymphs molted in two instances as 
soon as the eleventh day after dropping. The first instance occurred 
in a lot of ticks which dropped August 6, 1908. The mean tempera- 
ture during this period was 87° F., 485° F. of effective temperature 
having been required for this transformation. Most of the ticks 
from this same lot, which dropped on the same day, molted on the 
fourteenth, fifteenth, and sixteenth days. The second case, when a 
molting period of 11 days was observed, occurred with a nymph 
which dropped July 21, 1910. The mean temperature during this 
period was 89.5° F. and the total effective temperature was 511° F. 
There is a great variation in the periods required by this species 
for molting. Thus of 3 engorged nymphs which dropped May 20, 
1908, 2 molted to females on the seventeenth and eighteenth days, 
while the third did not molt to adult until the forty-ninth day after 
dropping. A still more marked variation in the molting periods of 
a group of ticks was observed in a lot of 3 nymphs which dropped 
October 3, 1909. Two of these molted on the eighteenth and nine- 
teenth days after dropping, while the third did not transform until 
March 22, 1910, or 170 days after dropping. Both of these lots were 
kept under identically the same conditions and all appeared to be fully 
engorged. In the second instance the molting of the last nymph 
