MICROSCOPIC OBJECTS. 79 



Fig. 157. Larva of the Bot-Fly as seen in the Egg (CEstrus 

 bovis), x40. 



This Fly is extremely hairy : the head is covered with light 

 yellow hairs ; the thorax is also yellow and barred with black, 

 the abdomen being partly black, but terminating in an orange- 

 yellow colour. The Fly is much dreaded by cattle when in 

 the open pastures. The insect generally lays its eggs under 

 the surface of the skin, with an ovipositor adapted to the pur- 

 pose ; but occasionally they may be found on the hairs of the 

 animal (see drawing) . After the larva is matured by living 

 on the flesh of the ox, it falls to the ground, and works under 

 a stone or buries itself; it then passes into the cocoon-state, 

 and in course of time emerges as a perfect Fly. The spiracle 

 of a Fly closely allied to this insect is drawn in fig. 154. 



The eggs, when found, may be soaked in turpentine, and 

 mounted with Canada balsam, in a cell so as to take off all 

 undue pressure. 



Fig. 158. Eggs of a Species of House-Fly (Anthomyia cani- 

 cularis) , x 40. 



The Flies of the genus Anthomyia closely resemble the 

 common House-Fly (Musca domestica], both in appearance 

 and habits; but unlike the House-Fly they do not quite restrict 

 themselves to habitations, being often found on plants of the 

 field. The eggs of this species are of great beauty ; they are 

 generally deposited in the ground. 



The eggs are best seen when mounted in a dry opaque cell. 



