8 



HARDWICKE'S SCIENCE-GOSSIP. 



in fig. 20, its diameter 5 ' 5 inch) were placed with a 

 portion of the meat in a glass vessel, and next day 

 the maggots had emerged as in fig. 21 (diameter ^ 

 inch), where the ramifications of the tracheal system 

 may be traced. 



The warm weather, coupled with the indoor heat, 

 matured the larva rapidly, the change from maggot 

 to chrysalis (fig. 19) being apparent at each observa- 

 tion, some having assumed this state on July 30. 

 The perfect stage was reached and the fly emerged 

 on August 5, or eight days from the deposition of the 

 ova (fig. 18). 



This was a week in advance of the result obtained 

 in my experiment, which I preferred to conduct out 



render the trachea, as well as the undulatory vermi- 

 cular movement of the internal organs, apparent 

 throughout under a low power 5 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 colour 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 becomes 

 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 impoverished, compared to those permitted to 

 feed in a semi-fluid mass of animal matter. 



F'g. 18.— The House-fly (Musca domestica), magnified. 



Fig. 20.— Egg of House-fly, July 28, 1878, X 30. 



Fig. 13. — Chrysalis of House-fly, July 20, 

 ^1878, X 40. 



Fig. 21. — Maggot of House-fly, July 29, 1878, X 25. 



of doors. A piece of raw liver was exposed, which soon 

 had eggs enough attached to it. It would appear 

 that the fly has to some extent the power of with- 

 holding the deposition of her ova until a suitable 

 medium is found for the requirements 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 odour 

 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 ; their leathery integument is not 

 easily ruptured, and is sufficiently translucent to 



In autumn the house-fly seems specially the 

 victim to the attacks of a parasitic fungus {Empitsa 

 Musca), 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 amongst 

 fish in aquariums, and last year even attacked salmon 

 in some English rivers. 



The cause of the fly becoming so firmly attached to 

 dry surfaces is this. The two pulvilli which, with two 

 strong curved claws (perhaps best seen with the flesh- 

 fly, Musca vomitoria, as a subject), terminate the foot 

 are surrounded by a fringe of tubular hairs, each ending 

 with a disc or sucker, through which a glutinous fluid 

 exudes. These form the points of attachment, enabling 



