for birds is most important for the survival and distribution of 

 these species. Bird migrations may be of extreme importance in 

 spreading certain ticks j in Egypt a considerable body of yet un- 

 studied data is being amassed on this subject. 



The apparent adaptability of some hyalommas and rhipicephalids 

 in altering the number and kinds of hosts they require when and if 

 the situation demands is a most important factor where the supply 

 of a variety of hosts is a critical factor of survival, which in 

 turn determines distribution. 



The only seriotis studies on African tick distribution are 

 those of Theiler (l9/h8,1949A,B,1950A,B,C,1956), Theiler and Robin- 

 son (1953A), and Theiler and Salisbury (1956), for South Africa. 

 In these, a combination of valuable criteria, i.e., vegetation 

 plus range, mean, and seasonal distribution of temperature and 

 rainfall, are carefully correlated with localities from which 

 ticks have been collected. Vegetation types are shown to have 

 a close kinship to outlines of tick distribution and the same 

 appears to be largely true in the Sudan. These reports should 

 be studied by anyone interested in the geographical distribution 

 of ticks. Theiler freqtiently mentions uneven distribution, an 

 aspect of the overall picture often most difficult to evaluate 

 because of the complex factors mentioned in the present brief 

 discussion. 



For epidemiological and economic purposes tick species to 

 be considered zoogeographically are more ntimerous than those that 

 majf be readily considered academically strictly as indicators of 

 zoogeographic Districts. Domestic animal parasitizing ticks, so 

 important from the standpoint of hvunan and animal diseases and 

 numerically so common in observations and collections, are often 

 more widely distributed than they might be in the absence of 

 domestic hosts. Similarly, host specific ticks of wild animals, 

 which are frequently those rapidly disappearing with the advance 

 of civilization and hunters, are becoming more restricted in 

 their contemporary range. In the following discussion an at- 

 tempt has been made to strike a functional medium from both the 

 practicaj. and the academic standpoints. 



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