FLIES. SCOLOPENDR.E. 



59 



17. The number of species of flies (Musca) is very great. 

 Their larvae feed on meat, carrion, &c. : they are in form of soft 

 whitish worms, and are frequently termed Maggots. 



18. The gad-flies ((Estrus) resemble large flies; their flight is 

 accompanied by a humming noise ; they are very tormenting to 

 horses, oxen, &c. ; some of them pierce the skin of these ani- 

 mals to deposit their eggs ; others simply lay their eggs in the 

 vicinity of one of the natural apertures of the body, and the 

 larvae in this manner at birth enter the stomach through the 

 nostrils or nasal sinus. The larvae of the CEstri are usually 

 conical and entirely destitute of feet; their presence in horses 

 constitutes the disease termed bots. 



CLASS OF MYRIA'PODA. 



19. The Myria'pods (from the Greek, murias, ten thousand, 

 and pous, foot) breathe air by means of tracheae, like insects, but 

 differ very considerably from these animals, as well as from 

 arach'nidans, in their general conformation. They never possess 

 wings, and the body, which is very much elongated and divided 

 into a great many segments or rings, bears on each ring, at least 

 one pair of legs; the number of these organs is twenty-four, or 

 even more, and there is no line of demarcation between the thorax 

 and abdomen. They bear some resemblance to serpents, or 

 rather to what worms would be if provided with legs, but their 

 internal organization is similar to that of insects. 



Fig. 55. SCOLOPEN'DRA. 



20. The head is furnished with two antennae and two eyes 

 ordinarily formed by the union of ocelli. The mouth is formed 

 for mastication. The number of rings of the body varies. They 

 experience while young an imperfect metamorphosis, but these 

 changes are not similar to those we observe in insects properly 



17 What are maggots? 



18. What are the characters of gad-flies ? 



19. What are the characters of the class Myria'poda ? 



20. To what description of metamorphosis are myria'pods subject? 



