Feb. '08] JOURNAL OF ECONOMIC ENTOMOLOGY 37 



The position of the genital pore varies from midway between the 

 front coxs to midway between the posterior pair. 



The ticks are naturally separated into three classes according to 

 their habits of molting as suggested by Ransom: first, those which 

 pass both molts upon the host, represented by members of the genus 

 Margaropus and by Dermacentor nitens; second, those in which the 

 £rst molt is passed upon but the second off the host, represented by 

 Ornithodoros megnini of this country and Rhipicephalus bursa and 

 ■evertsi, two South African species; third, those in which both molts 

 are passed off the host, as is the case with most of the ticks found in 

 this country. 



A fourth class might be recognized to include those which drop to 

 pass the first molt, but which remain upon the host for the second; 

 ;as yet, however, no representative of this class has been found. 



Of importance in connection with the transmission of disease is the 

 fact that while the first class pass the entire parasitic period of a 

 generation upon a single host, yet the second may attach to two and 

 the third class to three separate hosts. 



It will be seen that in the first class, where the ticks molt upon the 

 host and instead of having to wait long periods to find a host, they 

 merely continue sucking blood from the same animal. As a result 

 these ticks reproduce very much the faster and become of greater 

 importance as external parasites, where numbers and the removal of 

 blood are considered. This is the case with our fever tick. In the 

 'Class where both molts are passed off the host and a host found three 

 separate times for each generation their chances of reaching maturity 

 are lessened as compared with the first class by the proportion of 

 three to one. They have overcome this great disadvantage it would 

 •seem by having become more resistant to heat and cold and by having 

 gained the power to withstand much longer periods of fasting, as well 

 as by having acquired adaptation of habits. This will be discussed 

 under the heading of host relationship. 



While the representatives of the first class, all belonging to the 

 sub-family Rhipicephalinae, are more numerous, yet their greater 

 importance as external parasites is to some extent surpassed by the 

 third class, particularly by the members of the sub-family Ixodinae, 

 ■owing to the fact that the much greater lengths of the hypostome 

 permit of several times deeper penetration. As the result of this deep 

 penetration by the Ixodince, an inflammation is produced ofttimes 

 resulting in suppuration. Frequently in the attempt to remove ticks 

 belonging to this latter class from the body of the host, the capitulum 

 is separated from the body of the tick and remains embedded in the 

 3iost. Lounsbury reports that in some sections of South Africa dairy 



