of the epicuticular lipoid. The order of their resistance 

 is as follows: Ornithodoros moubata ; Dermacentor ander ~ 

 soni; D. reticiilatus ; Rhipicephalus san^uinexis ; Amblyoinma 

 cajennense and A, macuTatum ; Ixodes canisuga ; _I. hexagonusj 

 I. ricinus . In^dry air, water loss through the cuticle 

 IS ten to fifteen times more rapid in Ixodes ricinus 

 than in Dermacentor andersoni . The more resistant spe- 

 cies also take up water through the cuticle after desic- 

 cation; indeed, the rate of uptake over a unit area of 

 cuticle is approximately the same in all species of 

 Ixodidae. Uptake thus appears to be limited by the 

 ability of the epidermal cells to secrete water.'" 



As already stated. Lees has shown that 0. moubata is more re- 

 sistant to desiccation than nost ixodid ticks. Nymphs exposed to 

 dry {(^0 R.H^^fair at 25°C , survived for 35 days and lost only from 

 one to three percent of their original weight daily. This survival 

 period is strikingly longer than that of several ixodid tick spe- 

 cies used in the experiments. After a period of desiccation (five 

 days at ($> R.H.), 0. noubata regains most of its original body 

 weight when placed'in 95% K.H. for five days. Water is taken up 

 through the spiracles, for no increase occurred when these open- 

 ings were blocked. Loss of water occurs through the cuticle and 

 spiracles (see Spiracular Morphology and Function below). 



In order to carry Lees* work one step further. Browning (1954B) 

 conducted a study on the exchanges of water between the atmosphere^ 

 and 0. moubata . Unfed nymphs were able to abstract water from moist 

 air T95/^ ti.U.) and to restrict their rate of water loss in dry air. 

 This ability was lost (a) in atmospheres containing 3Q& to U5% CO2; 

 (b) in atmospheres containing more than 9Qfo N2; (c) immediately after 

 the tick fed; and (d) gradually after the tick has been starved for 

 some five months. It was shown that the action of high (3C^ to 

 U%) concentrations of CO2 is mainly upon the activity of the epi- 

 dermal cells, possibly mediated through the central nervous system. 

 The concentration required to cause opening of the spiracles is only 

 about five percent. These findings are of considerable interest in 

 relation to Lees' (19A.7) basic work. 



By way of introduction to his 19A-7 study. Lees stated: 



- 153- 



