214 NATURAL HISTORY OF AQUATIC INSECTS CH. 



now and then touched the water with her legs. When 

 satisfied as to the suitabiHty of the place, she alighted 

 a few inches above the water-level, and extended her 

 abdomen considerably. The pointed and curved ex- 

 tremity was several times protruded and again re- 

 tracted. Then the female flew or walked away, and 

 repeated the operation in a fresh place. On search- 

 ing the spots where the fly had settled, which were 

 usually in the crevices between the staves of the 

 bucket, eggs, sometimes to the number of twenty, 

 were found attached to the wood. They were white, 

 of oblong shape, and not unlike those of the Blow-fly ; 

 the surface was finely shagreened. The eggs were 

 viscid, and adhered to the wood. 



Living trees often contain cavities formed by decay. 

 When these become filled by rain water, they form 

 favourite sites for the egg-laying females, especially 

 in autumn. One species which is found on trees has 

 the larval tail much shorter than common. Before 

 pupation the larva attaches itself to some object by a 

 viscid exudation from the skin. In another species 

 which also passes its larval stage in the cavities of 

 trees the tail is very short, and flanked by a pair 

 of conical fleshy promiinences. At the extremity of 

 the tail the two posterior spiracles are plainly to be 

 seen. At the head end are two small yellowish 

 projections which also communicate with the tracheal 

 trunks. These are the anterior spiracles. A little 

 behind these and more external comes a pair of 

 double hooks. There is also at the extreme fore end 

 of the body, and just above the mouth, a pair of 

 fleshy prominences, as in other rat-tailed maggots. 



