PARASITISM 



335 



female, however, inserts its proboscis into the 

 skin once for all and attaches itself so firmly that 

 it cannot be pulled loose without tearing away 

 its mouth parts. It does not let go until it is 

 completely filled and has been fertilized by 

 the male when it drops off to lie helpless on 

 the ground, where after a short time it dis- 

 charges a large mass of round transparent 

 eggs from which the embryo ticks hatch. 

 Where ticks are numerous they may be trouble- 

 some. They may attach themselves without 



FIG. 117. Ornithodorus moubata. Tick that transmits African relapsing fever: 

 a, Viewed from above; b, viewed from below. (Robert Koch.) 



any sensation or disturbance of the host, or 

 their bites may cause intolerable irritation. 

 Their chief importance depends upon the fact 

 that they harbor certain parasites which they 

 transmit from animal to animal, not always 

 directly, since they rarely visit more than 

 one host, but by taking the parasites from 

 the animal frequented, and passing them 

 through the eggs to a new generation through 

 which new animals become infected. It is in 

 this manner that the "Texas fever" of cattle, a 



