296 ZOOLOGY. 



conditions in one locality may change the balance of life in another. The 

 second chapter of the prophet Joel gives a vivid account . of a visitation 

 of locusts. See Fig. 137. 



Order Neuroptera (nerve-wings). The members of this order have 

 a more or less complete metamorphosis. Two pairs of netted membranous 

 wings. The mouth parts are suited to biting. Here we may include the 

 social termites or white ants, the may-flies, whose adult life usually lasts 

 onl / for few hours, and the carnivorous dragon-flies. 



FIG. 139. 



FIG. 139. Larvae of the Bot-fly (Gastrophilus equi) in the stomach of the horse. One 

 half natural size. From Luggar, after Heller. 



Questions on the figure. What do you know of the habits of the bot- 

 fly? Where are the eggs deposited? How do the larvae come to have 

 the position figured above? How do they pass from this to the adult 

 condition? See also Fig. 140. How does it retain its position in the 

 stomach of its host? 



Order Hemiptera (half-wing}. Hexapoda with an incomplete meta- 

 morphosis, and having two pairs of wings, or none. Mouth parts are 

 modified for piercing and sucking. Here are included the true bugs, as 

 the squash bug, the water boatman, etc. ; the lice ; the plant-lice ; and the 

 cicadas (sometimes called "locusts"). These should not be confused with 

 the beetles, which are often called " bugs." See Fig. 138. 



Order Diptera (two wings}. These Hexapoda undergo a complete 

 metamorphosis, having the anterior pair of wings developed (not in fleas). 



