Feb. '08] JOURNAL OP ECONOMIC ENTOMOLOGY 39 



with the exception of the dog, it attaches to almost all domesticated 

 mammalia. 



Mammals serve as the principal hosts of the ticks. Fowls are 

 largely the hosts of the genera Argas and Ceratixodes, and of one or 

 two species of the genus Haemaphy sails. Several species of the 

 genera Ixodes, Amblyomma and Hyalomma are also parasitic upon 

 fowls. The reptiles are not immune, several species attaching to 

 them. 



Adaptations as factors in Host Relationship. — It cannot be 

 doubted that a great evolutionary process has taken place in the 

 adaptation both of structure and of habits as related to reattachment 

 and protection. It is not the intention of the writer at this time to 

 enter deeply into a discussion of this matter but merely to mention 

 the result of this great natural process as he sees it. This evolutionary 

 process or survival of the fittest has resulted in the special adaptation, 

 first of function and structure, and second of the habits of ticks. 



All ticks must find hosts and attach at least once, some as many 

 as four times. This necessity has resulted in Special adaptation of 

 function and structure for attachment. An illustration of this adap- 

 tation of function is found in the way the Ixodids use the front pair 

 of legs. As one approaches the free tick these legs can be seen waving 

 in the air, while with the others it holds to its support. When a 

 host comes in contact with them they cling to it most tenaciously with 

 these legs. To determine the fact one has but to pass a finger rapidly 

 over a cluster of the seed-ticks. The adaptation of structure for pro- 

 tection is represented by the engorged larvae of Argas mimatus or 

 persicvs. Up to within a few hours of dropping these larvfe are 

 globular in shape, but at this time they flatten and assume the typical 

 Argas shape ; this flattened form, natural to all of the other stages, 

 permits the ticks to crawl rapidly and to secrete themselves in cracks 

 and crevices protected from the wily fowl. In the Ixodince we find 

 what may be considered specially adapted mouth parts, which being 

 unusually long, penetrate deeply and prevent their being easily 

 removed. 



In the adaptation of habits favorable to attachment and protection 

 we find most striking illustrations of the great process of natural 

 selection. The adaptation of habits favorable to attachment may be 

 placed in four classes: first, in molting; second, in attachment to any 

 host ; third, of habits to habits of host ; and fourth, in acquired greater 

 vitality. There is a great disadvantage in dropping to molt, for it 

 necessitates long periods of waiting, and results in a high percentage 

 of mortality from not finding the host. This disadvantage seems to 

 have been overcome by some species which have acquired the habit of 



