254 DIPT ERA. 



fly is largely due to the rapid vibrations of the wings/ 

 and it may be, in lesser degree, to the spiracles of the 

 thorax. 



The development of Tabanus has not been fully 

 worked out. The larva of one species is of large size, 

 measuring nearly two inches in length ; the head is 

 retractile and is provided with jaws. Along the body 

 are projections or warts used in locomotion, and at 

 the end are fleshy processes. 



The development of the house-fly has been de- 

 scribed and figured by Packard.- The eggs are laid in 

 the manure of stables, and under favorable conditions 

 require about twenty- four hours for development ; but 

 when the heat and moisture are not sufficient, the 

 time is longer, and the larva is smaller when hatched. 

 PI. XII., Fig. 200, is a dorsal view of the young larva, 

 or maggot, as it is usually called. The two main 

 tracheae are represented with the anterior and pos- 

 terior commissures (//^). PI. XII., Fig. 201, is the 

 larva after it has moulted once. It is not a general- 

 ized, but an extremely specialized form. Although 

 living in such soft substances, it is, nevertheless, a 

 boring creature, and the head is therefore small and 

 suitable for penetration, the propelling power being 

 placed in the larger, posterior end. The body con- 

 sists of a succession of similar rings without feet, but 

 with set?e to help the animal when boring. 'PL XII., 

 Fig. 203, shows the forward end, which is not differen- 

 tiated into a head ; at are the antennae. The man- 



1 See Burgess, " Recent Studies in Insect Anatomy," Psyche, 

 Vol. III., No. 71, March, 1880. 



2 Proc. Post. Soc. Nat. Hist., Vol. XVI., 1873-74. 



