150 



PARASITES OF THE DOMESTIC ANIMALS 



ried on upon this portion of the tick's Hfe 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. 



Length of Period and Total Duration of Parasitic Development 



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 animals 

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



