64 



thrusts them into the dung. This keeps the coat of 

 the egg soft, otherwise the embryo could never got 

 out; but if the whole egg were thrust :n, the creature 

 would be suffocated as soon as it is hatched ; therefore 

 part only is to be immersed, and part (o be left out, 

 and this is admirably provided for by these wings; for 

 when the female thrusts in the egg, it easily enters at 

 the smaller end, which is the part first protruded from 

 her body ; but it stops at (he wings, and so the upper 

 part remains open to the air. 



Some species of flies fasten their eggs to the sides of 

 vessels of water. All these eggs have a thin flake run- 

 ning down the two sides diametrically opposite, so that 

 they look as if they were enclosed in a frame. The 

 use of this frame is, to hold the body of the egg more 

 firmly to the side of the vessel. Tiio.se eggs which have 

 it not, are deposited by the female fly with a viscous 

 matter about them. 



Some flies lay their eggs in the bodies of caterpillars. 

 These are at great pains to carry those caterpillars to 

 the places where it is proper their eggs should be 

 hatched. There is one species whose worm can ne- 

 ver succeed, unless it be both bred in the caterpillar, 

 and that caterpillar buried under ground. To this 

 purpose the parent, when ready to lay her eggs, forms 

 a hole in the ground, and covers it w^th a little clod ; 

 then she goes in search of a proper caterpillar, per- 

 baps one much larger than herself, which nevertheless 

 she drags to her hole : this she uncovers, and goes in 

 to see if all is right ; then she goes and draws the ca- 

 terpillar in, deposits her eggs in his flesh, and stops 

 up the hole with several pellets of dirt and dust, care- 

 fully rammed in between. When the worms are 

 hatched, they feed on the flesh of the caterpillar till 

 they are full grown : tuen they change into aurelia, 

 and afterward into the form of the parent-fly, in 

 which state they easily make their way out of the 

 ground. 



Some of these lay their eggs in the bodies of smaller 

 flies. Itiey often fly with one of them ia their legs, 



