318 



BIOLOGY: GENERAL AND MEDICAL 



Ixodiodea. The eggs usually hatch upon the 

 ground yielding six-legged "nymphs" or larval 

 forms. With the second moult they acquire a 

 fourth pair of legs and become mature. The 

 young ticks climb the stems of plants and there 

 await the coming of some warm-blooded animal 

 to which they quickly transfer themselves. 

 The proboscides of the little ticks cannot reach 



1 



FIG. 112. Pyroplasma bigeminum. Cause of Texas fever in cattle, in 

 stained blood of steer. X 1000. a. Leucocyte; 6, normal erythrocyte; c, 

 erythrocyte containing one pair, d, erythrocyte containing two pairs of pyro- 

 plasmata. 



the blood, but their introduction into the skin 

 sets up an inflammatory reaction with some 

 edema and the lymph nourishes them. The 

 bites sometimes suppurate. When full-grown 

 the proboscis easily penetrates the skin, and the 

 parasites slowly distend themselves with blood 

 to a surprising extent. The male tick does 

 not seem to be much of a blood sucker, bites 

 occasionally, and is satisfied with little; the 



