216 



OUR HOUSEHOLD INSECTS 



flies in our regions, so that they have it all to them- 

 selves, with little competition, the numerous beetles 

 that have similar habits being said to feed quite as 

 much on the fly-larvse themselves as on the carrion. 

 Their action must, from the nature of the case, be 

 rapid, and the supply of food he regards as plentiful. 

 All these conditions .favour multiplication, and have 

 contributed towards producing the extraordinary fecun- 

 dity for which the insects are noted. There is one other 



FIG. 70. A, Portion of Left Ovary of Bluebottle, containing about eighty 

 Eggs. , Side View of Portion of Eight Ovary, showing Distribution of 

 Tracheae, or Air-Tubes (), to the Organ. 



point which lessens the competition, viz., that the 

 different species to some extent succeed one another 

 during the summer in point of time (i.e., in the larval 

 form), instead of being contemporaneous. This was 

 proved in the following way: he laid out of doors 

 the dead bodies of small vertebrates, such as rats, birds, 

 &c. The flies soon laid eggs upon them, and these 

 were then collected and the maggots bred to maturity, 

 whereby the relative numerical abundance of the species 

 was ascertained. One of the chief results thus estab- 

 lished was that Cynomyia mortuorum, an out-door 



