APTEEA. 251 



its egg in the water on any floating substance, the 

 larva which comes from the egg is aquatic, living 

 with its head downwards, the end of the abdomen only 

 being above the water, in this there is a spiracle or 

 breathing orifice, which enables it to take in the air ; 

 the Gnat, when it comes from this larva, stands on its 

 shell for a moment, and then flies oif, for it is not 

 suited to live in the water ; this history of the early 

 stages of its life, accounts for Gnats being always found in 

 such numbers near pools of water. The Tsetse, which 

 Dr. Livingstone describes as being so fatal to cattle, is 

 of this order ; he says, " It is well known that the bite 

 of this poisonous insect is certain death to ox, horse, 

 or dog. ... A most remarkable feature in the bite of 

 the Tsetse is its perfect harmlessness to man and wild 

 animals, and even calves, so long as they continue to 

 suck the cows." 



9. APTEEA (Wingless). 



To this order belongs the Flea (Pulex irritans), which is 

 furnished with lancet-shaped weapons, through which 



PIG. 30. PLEA (Pulex irritans) 



it sucks the blood of other animals, for it is entirely 

 parasitic, and also the " Chigeo " (Pulex penetrans), 

 which is a troublesomo and even dangerous pest in the 

 West Indies ; it penetrates the skin of the feet, and 

 deposits its young beneath it. 



The last class of the Articulata, the Arachnida, includes 



