ECONOMIC ZOOLOGY — ENTOMOLOGY. 751 



10 days for nymphal engorgement, and 4 to 14 days for the final, or adult, 

 engorgement. The nonparasitic stages vary greatly with the season and tem- 

 perature. The preoviposition period may last but 2 days in midsummer or it 

 may be prolonged to 56 days in winter and spring. The oviposition period 

 varies from 9 to 122 days under similar conditions. . . . 



" The alimentary system of the tick consists of from 10 to 12 c£eca, or blind 

 sacs, which provide large storage capacity. Movement of the food particles 

 within these caeca is accomplished by peristalsis. No waste materials are ex- 

 creted by the adult tick after final engorgement. Such materials are stored in 

 the renal sac and the Malpighian tubes, mostly in the form of crystals of uric 

 acid, which remain there after death. . . . 



" The rate of oviposition varies with temperature. The average daily rate for 

 26 engorged ticks kept in the incubator at 85° was 285 eggs, the extremes 

 being 156.8 and 407.1 eggs, respectively. The average number of eggs produced 

 by each individual tick was 2,113, varying from 967 to 4,071 eggs. The largest 

 number produced within any 24-hour period by a single tick was 1,006 eggs. 



" Engorged adult ticks exposed to temperatures of 24° or lower may be killed 

 by freezing. Those under dry conditions will survive temperatures fatal to 

 those under moist conditions, while partly spent females are more easily killed 

 by cold than those that have not yet begun egg laying. Ticks protected by a 

 covering of dry litter will survive very much more cold than those not so pro- 

 tected, but moist litter offers no protection at all. 



"Eggs protected by the viscid secretion from the shell glands retain their 

 moisture very much longer than those without it. Those eggs from which this 

 coating has been washed are liable to absorb sufficient water to destroy the 

 embryos, if they remain submerged. 



" The incubation period of the eggs varies from 24 days, the record of a lot 

 of eggs laid by ticks dropping from the host on July 5, to 252 days for eggs 

 laid by ticks maturing September 20. Eggs laid by ticks dropping from the 

 host before August 28 will hatch before winter, while of those laid by ticks 

 dropping after this date a few may hatch the same season, the remainder going 

 over until the following spring. Whether they will hatch then depends upon 

 the effectiveness of the viscid coating of the eggs in preventing excessive loss 

 of moisture. Probably many of the eggs exposed to extreme cold are destroyed. 

 In our experiments all eggs exposed to 2° F. were killed. It is very difficult, 

 however, to dissociate this effect from that of excessive drying during the long 

 dormant season. . . . 



" The six-legged seed ticks immediately after emergence are able, if necessary, 

 to fast for several months while awaiting a host animal. Our record of great- 

 est seed-tick longevity is 298 days. . . . Seed ticks hatching from eggs laid by 

 engorged ticks dropping during July live longest, while those from September- 

 maturing ticks are the shortest lived, the longevity in this case being about 

 one-third that of those from July ticks. . . . The average longevity of seed 

 ticks hatching from overwintering eggs is 94 days, while that of seed ticks from 

 eggs hatching before winter is 176 days. This indicates a debilitating effect on 

 the developing embryos, due to cold and drying during the long dormant season. 

 Seed ticks are able to survive the ordinary winter temperature of the tick area, 

 except along the northern border. A temperature of 4° F., however, is fatal 

 to all seed ticks." 



A table is appended which gives detailed information concerning the 2,315 

 engorged female ticks kept under outdoor conditions at Knoxviile, on which 

 the facts and conclusions reached in this bulletin are based. 



A list of 15 titles of the literature referred to is appended. 



