484 INFLUENCE OF CLOIATE ON ANIMAL DISEASE. 



1899, Lounsbiiry said that it was known to occur from Hunians- 

 ■dorp and Uitenhage in the Cape Province, eastward to Natal, 

 and inland for about 50 miles from the coast, and that it ])rob- 

 ably occurred for a long distance up the East Coast. He also 

 stated that it was recognised prior to 1835 in Lower Albany, 

 being then regarded by the farmers there as a curiosity. I'ii 

 the Transvaal Theiler has pointed out that this tick is limited 

 to the bushveld proper, occurring only in those parts of the low 

 veld where real bush is met with, and not appearing in the 

 middle veld. This point will again be referred to, and it is cliiefly 

 because of this limitation of distribution that 1 have introduced 

 this tick here, but at the same time it is very interesting to note 

 ■certain ])oints in connection with its life-history. 



Thus we may mention that, according to Theiler, the period 

 occurring between the dropping of the engorged female from 

 the host and the laying of eggs may vary from two weeks in 

 summer to three months or more in winter time, and the eggs 

 •deposited may hatch at the earliest in summer -in about 10 to ii 

 weeks, whilst in winter this may only occur in as many months. 

 Lounsbury states that if kept too dry and >\arm, the eggs may 

 •cave in all along one side and shrivel up, but that it takes very 

 little moisture to keep them alive, and that hatching does not 

 •depend on rain, as is often popularl\- believed. The period 

 occupied by the moult from the larval to the nym])hal stage is 

 from 25 days to four months under natural conditions, accord- 

 ing to Theiler, and Lounsbury has shown that where this process 

 was artificially hastened in the incubator the jjcriod occupied was 

 reduced to 16 days. In two batches of ticks ke])t in a sunny, 

 sheltered place during the daytime, and placed indoors at night, 

 this latter observer noted that moulting at this stage did not 

 occur until seven winter weeks had expired, and he therefore 

 believes that under veld conditions in the Cape Province the 

 period must vary with season and situation probably from one 

 to three months. The engorged nymph in moulting to the adult 

 stage may take, according to Theiler, from about 25 days in the 

 summer and t6o days in the Avinter in the Transvaal, whilst in 

 the Cape Province Lounsbury noted that the period was variable, 

 and that whilst in one individual of one batch of ticks the 

 nymphal skin ruptured as early as the eighteenth day, in another 

 batch this only occurred about the eleventh week-. 



These facts will suffice to show the importance of climatic 

 and tellurical factors in affecting the development of these ticks, 

 and similar observations pointing to the great importance of 

 heat and the lesser importance of moistitre on tick development 

 have been made on the same and numerous other' species in 

 many parts of the world, and largely in Europe and America. 



Enough, however, has been said to explain the points which 

 are of special interest to us in considering the prevalence of the 

 diseases transmitted by these arachnids. It is. for instance, now 

 not difficult to understand the greater prevalence of tick-borne 

 diseases during the months of summer and autumn as compared 



