150 



PARASITES OF THE DOMESTIC ANIMALS 



ried on upon this portion of the tick's life history tick-free animals were 

 infested at nine different times from July, 1907, to May, 1908. It was 

 found that the minimum larval period ranged from five to seven days; 

 the minimum nymphal period of females, nine to eleven days; the adult 

 period, from a minimum of five to a maximum of thirty-three days. 

 The table which follows is given to show the range of the periods ob- 

 served upon larvae which were marked after they had become attached 

 and then kept under observation from day to day. 



As to the importance of the foregoing data, Graybill says: ''The dura- 

 tion of each of these stages and the duration of a single infestation upon 

 cattle during different portions of the year are of great practical im- 

 portance. Upon the duration of an infestation depends the time anmials 

 must be kept on tick-free fields in order to become free from the ticks." 



