32 The Philippine Journal of Science wis 



The egs is creamy white and of the ordinary muscid type, 

 with its convex side adhering to the place of attachment when 

 laid. The grooved concave side through which the larva makes 

 its exit is conveniently considered the dorsal side. The length 

 of the egg averages 1 millimeter. There is no appreciable 

 change either in color or form during incubation, which under 

 ordinary conditions takes from twenty to twenty-six hours. 



THE PROCESS OF HATCHING 



In observing the hatching microscopically, it is quite neces- 

 sary for the best results to suspend the eggs in a moist medium, 

 preferably, physiological salt solution. When fertile eggs are 

 placed in the air on a dry slide for as long as one hour, the 

 hatching which has begun is inhibited and the embryo dies 

 within the egg. 



A certain sign of sterility, which can be applied as a test for 

 eggs of this species, is the absence of embryonic movement 

 within tv\^ days. There is not a distinctive dark polar spot, 

 and the color changes to a dull pink, then rose, followed by 

 brown after two days. If some moisture is present, the sterile 

 egg ordinarily does not shrivel. 



The movements of the embryo usually cannot be observed 

 until the last four hours of incubation, when the cephalic area 

 becomes ash-gray and gradually darkens as the movements 

 become more active. The usual dilatation and contraction of 

 the chorion take place accompanied by the occasional movement 

 of the amniotic fluid. 



Two pharyngeal spines, which appear under the cuticle, curved 

 slightly posteriorly on the pharyngeal apophyses assist the 

 embryo to escape from the egg. Prior to the process of hatch- 

 ing, the embryo lies curled up, and as the body gradually 

 straightens out the head capsule extends from its sinus bring- 

 ing the hatching spines into contact with both slits of the 

 micropyle canal, the cephalic end of which is neatly carved out, 

 laying open a flap of the chorion of the egg. By means of 

 pressure from the posterior end and a constant prodding of 

 the head appendages, the micropyle canal is forced open and 

 the larva glides through the opening. 



The ova are very sensitive to changes of temperature, light, 

 and humidity. Incubation can be lengthened to fully double 

 its normal length by lowering the temperature or by withdraw- 

 ing the moisture from the medium in which eggs are laid. 

 Exposure to light also influences the metamorphosis of this 

 fly. At a room temperature of 30° to 31° C, eggs hatch in 



