344 Appendix II [66] 



Summary. 



A consideration of the facts presented in the foregoing pages 

 appears to warrant certain conclusions which must, however, be regarded 

 in part as provisional and subject to revision when our knowledge of 

 the various species of ticks has become more extended. The views 

 here expressed may prove of practical use in the study of the Ixodidae. 



The Argasidae represent the relatively primitive type of ticks 

 because they are less constantly parasitic than are the Ixodidae. Their 

 nymphs and adults are rapid feeders and chiefly infest the habitat of 

 their hosts. In certain Argasidae (0. moubata and 0. savignyi) the 

 disadvantage of their possessing an "active" larval stage has resulted 

 in the development of an " inactive " larva, i.e. the young nymph being 

 the first to suck blood. In 0. megnini we have a considerable adaptation 

 brought about by the difficulty there must be in the tick entering the 

 small aperture of the ear more than once. Owing to the Argasidae 

 infesting the habitats of their hosts, their resistance to prolonged 

 starvation and their rapid feeding habits, they do not need to bring 

 forth a large progeny, because there is less loss of life in the various 

 stages, as compared to Ixodidae, prior to their attaining maturity. 



The Ixodidae are more highly specialized parasites than the pre- 

 ceding. The majority are parasitic on hosts having no fixed habitat 

 and consequently all stages, as a rule, occur upon the host. In the 

 genus Ixodes we find an adaptation of certain species according to the 

 habits of the hosts upon which they are parasitic. In the species which 

 usually occur upon wandering hosts both sexes are found upon the 

 host, whereas in other species which occur on hosts possessing more or 

 less fixed habitats the males are rarely or never found upon the host. 

 The males of species of Ixodes, both sexes of which occur upon the host, 

 are characterized, as a rule, by the possession of hypostomes with 

 prominent teeth, the reverse being the case in forms wherein the males 

 do not occur upon the host. Where species occur upon a wandering 

 host it is essential, for their propagation in nature, that both sexes 

 should be carried about upon the host. 



It appears to follow that the copulation of ticks upon the host is an 

 indication of a higher degree of specialization to a life of parasitism. 

 When copulation does not take place on the host, we have merely the 

 retention of a primitive character as found in Argasidae. From the 



