February, '13] TICK DISCUSSION 95 



the ticks may be informed of the presence of a host by feeling its 

 breath and that they may avoid being taken into the mouth with the 

 food of animals, by dropping when a hot breath is felt. In a few 

 instances this tick has been seen waiting on green grass in our large 

 open-air cages, but this is exceptional and dead stems are distinctly 

 preferred by the adults. If the selection of dead rather than living 

 vegetation as supports is a fixed habit, it doubtless serves as a pro- 

 tection against being destroyed in the mouths of animals. 



Repeated attempts were made at stimulation by the heat or odor 

 of the hand applied at the top of the cage about five inches away from 

 the ticks but without success. 



President W. D. Hunter: We are now ready for the discussion 

 on this paper. 



Mr. E. C. Cotton: I would like to ask Mr. Cooley if he ever has 

 detected any indication of a sense of smell by this tick. 



Mr. R. a. Cooley: I have not detected any evidence of the sense 

 of smell in this tick. We had this sense in mind when we tried to 

 stimulate the individuals in the cage by placing the hand close to the 

 top, thinking that the heat or odor might arouse them. The results 

 were negative. 



President W. D. Hunter: Professor Cooley's work reminds us 

 that remarkable progress has been made in the study of the adaptations 

 of ticks. In fact, our knowledge of adaptations in this group is rapidly 

 becoming more complete than among insects proper. Heretofore 

 the contributions that have been made have dealt largely with struc- 

 tural adaptations but Professor Cooley's contribution deals with one 

 of a physiological character. These extreme adaptations are not 

 surprising in view of the inability of the tick to move about and its 

 necessity for waiting until a suitable host appears. The longevity 

 of one stage of the spotted fever tick has been determined to be over 

 six hundred days. Evidently the physiological adaptation to which 

 Professor Cooley has called attention is an effort on the part of the 

 organism to reduce this long period of waiting by extreme activity in 

 the presence of a possible host. 



A Member: Will the cattle tick when it climbs up spears of grass 

 show similar habits? 



Mr. E. C. Cotton : In the case of the cattle tick we have a different 

 situation for here it is the seed tick stage we find on grass instead of 

 the unengorged adult. The seed ticks occur in large clusters, as many 

 as 2,500 in a bunch instead of singly as with the unengorged adult of 

 the spotted fever tick, therefore it is more difficult to observe indi- 



