BY T. HARVEY JOHNSTON AND M. J. BANCROFT. 305 



During the period 1915-1918, Mr. Hull sent down 

 engorged ticks from various cows, both resistant and noi- 

 Tesistant, Avhose names were indicated by him. 



Of course one found many ticks that did not lay, also 

 many which laid few eggs and many which laid a normal 

 number of eggs from which no larvse hatched, but there 

 were quite enough normal hatchings in the case of eggs of 

 ticks from resistant animals to justify the above remarks. 

 On several occasions we noticed that, thoiigh under exactly 

 the same conditions, there Avas a very marked difference in 

 the activity of larvae, those whose parents w^ere taken from 

 ordinarj- cattle being much more lively and living much 

 longer that those from resistant animals. This may perhaps 

 be an individual matter as far as the parent ticks were con- 

 cerned. 



We have, then, had plenty of opportunity to test the 

 fertility of such ticks. We have already emphasised the 

 fact that extremely few ticks mature naturally on such 

 animals. In regard to such engorged ticks, we found that 

 the percentage of those with normal fertility was less than 

 in the case of ticks from control animals. The percentage 

 of those whose eggs did not hatch was practically the same 

 in the two sets. The same statements apply to the "' winter 

 ticks " spoken of by Mr. Hull— i.e., cattle ticks taken by 

 him from resistant animals during the winter. 



Mr. Hull carried out the following experiment. A 

 solitar}^ engorged tick was found (11/12/16) on a resistant 

 animal (Sunset). There was normal egg -laying and hatch- 

 ing, the larvae being applied on 10th Februarj', 1917, to 

 another resistant cow at the base of the tail. The infested 

 area was observed twice daily. The larvse became attached 

 especially in creases of the skin. On 19th February only 

 80 nj'mphs could be counted. Next day several males 

 and two nymphs were to be seen. Only one female reached 

 maturity. 



We carried out a similar experiment (January and 

 February, 1918) the results of which (detailed under cow 

 Squib) agree with those stated above. 



We would like to draw attention to the results obtained 

 by Bishopp and Wood (1913, pp. 176-178), who applied 

 iarge numbers (700-1,500) of larvae of Dermacentor 



