1873.] 137 [Packard. 



horse's and fowl's dung, especially when warm. He does not, how- 

 ever, state how long it remains in this state. After a fair description 

 of the pupa-case, he says that it remains in this state from eight to 

 fourteen days. His figures of the larva and pupa-case are very poor, 

 not being recognizable; but this is the only time, so far as we are 

 aware, that the insect has been figured in its preparatory stages. 



We have been unable to find any other references, of any import- 

 ance from a biological point of view, to this commonest of insects. 



Embryology. During the month of August the House Fly is ex- 

 tremely abundant, and as we, and others, have noticed, especially so 

 in the neighborhood of stables. On placing one fly in confinement 

 in the shade, enclosed in a glass bottle, she laid some time between 

 six p. m., August 12th, and eight a.m., August 13th, one hundred 

 and twenty eggs. They were deposited irregularly in stacks, as it 

 were, lying loose in one or two piles at the bottom of the bottle. At 

 eight a. m., August 14th, several were found hatched out and crawl- 

 ing about the bottom of the bottle. 



In order, however, to obtain a large number of eggs, we placed a 

 mass of freshly dropped horse manure, still warm, at an open window 

 in the sun. This attracted large quantities of flies for three or four 

 weeks succeeding, which laid eggs during that period. Immediately 

 on exposing the manure on the morning of the 12th of August, the 

 flies appeared and laid their eggs in masses in the crevices in the 

 manure, working their way down mostly out of sight, and depositing 

 bunches of eggs in various convenient places. These were found 

 hatched out at about the same hour the next day. From several 

 such experiments made on different occasions, we may regard the 

 embryo as requiring twenty-four hours for perfection. In confine- 

 ment it requires from five to ten hours more, and those larva? hatched 

 in confinement are smaller than those reared from eggs deposited in 

 warm manure. It is evident that heat and moisture are required for 

 the normal development of the larva, as usual in all insects. Thus 

 the egg state lasts for twenty-four hours, about the time of that of 

 Musca vomitoria, according to Weismann, 1 who states that it lasts 

 from seventeen to twenty-six hours. 



The egg is elongate oval cylindrical, a little smaller, more pointed 

 at the anterior end than the posterior. It is .04-.05 inch long, and 



1 Die Entwickelvmg der Dipteren im Ei, nach Beobachtungen an Chirononius, 

 Musca vomitoria imd Pulex canis. Zeitschrift fur Wissenschaftliche Zoologie xin., 

 p. 107-204. 1864. 



