PARASITOLOGY. 31 



tumors are formed, with holes at their summits. 

 The holes become larger as the tumors and larvae 

 develop. The larval stage lasts ten months. In 

 this stage they are called grubs, or warbles. By 

 spring they have developed into full-grown larvae, 

 and leave the tumors through the holes in the 

 summits. At this time they are three-fourths to 

 seven eighths of an inch long, and nearly one-half 

 inch thick. It has been observed that they leave 

 behind a tough brown or black skin. They bur- 

 row into the ground and pass through the pupal 

 stage in from four to six weeks. 



Animal Attacked. — The ox. 



Parts Infested. — Oesophagus and sub-dermal tu- 

 mors in region of back. 



Injury to Host. — Some irritation. If attacked by 

 large numbers the animal does not thrive. In those 

 cattle that are slaughtered during the grubby season 

 there is a great commercial loss to hides, on account 

 of the holes in the skin. The percentage of cattle 

 infested varies from practically none in the northern 

 states to seventy-five or eighty percent in the south- 

 ern states. 



THE FLEAS. 



PuLEX Irritans (Pulex — flea, irrito — to excite). 



Synonym. — Human flea. 



History. — ^Common in dwellings in Europe. Found 

 in the United States, particularly on Pacific coast. 



Description. — Body flattened from side to side ; 

 head small and rounded; stylet arranged for piercing 

 the skin and sucking the blood; two eyes and two 

 antennae. The abdomen is provided with nine rings. 



