DEVELOPMENT OF THE HOUSE-FLY. 619 



deposition of her ova until a suitable medium is found for the require- 

 ments of the larva. 



In two or three days the maggots were at work ; their activity and 

 voracity in devouring the putrescent mass of animal matter gave it the 

 appearance of fermentation. 



For observation in the live box, any little weakness connected with 

 the somewhat objectionable odor arising from the garbage had to be 

 got rid of and some few maggots washed clean. Neither immersion in 

 water nor yet compression seemed to inconvenience them appreciably ; 



Fig. 2. Chrysalis op House- 

 Fly, July 20, 1878, x 40. Fig. 3. Egg of House-Fly, July 28, 1878, x 30. 



their leathery integument is not easily ruptured, and is sufficiently 

 translucent to render the trachea, as well as the undulatory vermicular 

 movement of the internal organs, apparent throughout under a low 

 power ; in fact, from its toughness, transparency, and strength, the 

 larva is an excellent object for microscopic examination. When the 

 animal matter was devoured, the maggots moved restlessly about, 

 changing in color from yellowish-white to brownish-red ; the cuticle 

 became dense and opaque ; motion gradually ceased, until the perfect 

 insect emerged by forcing of the segments of the anterior end of the 

 shell, occupying from fourteen to fifteen days in completing its series 

 of life-changes. 



Mr. Harkus's part of the experiment appears to be useful so far as 

 to show the adaptability of the fly and its ova to circumstances, and 

 that the larva assumes the chrysalid state when its supply of food be- 

 comes exhausted, although otherwise immature (in this case the animal 

 matter given them would dry up), instead of dying from starvation. 



The chrysalis and fly in his examples are undersized and impover- 

 ished, compared to those permitted to feed in a semi-fluid mass of ani- 

 mal matter. 



In autumn the house-fly seems specially the victim to the attacks 

 of a parasitic fungus {Ernpusa muscce), and may be seen glued, as it 

 were, to walls, a white powdery growth appearing at the segments of 

 its body (the spores of the fungus). This vegetable pest is similar to, 

 if not identical with, the parasite which causes so much destruction 

 among fish in aquariums, and last year even attacked salmon in some 

 English rivers. 



