(66) 



506 0. GORDON HEWITT. 



that oviposition may take place as early as the fourth day ; 

 Taschenberg (t. c.) states that the female lays on the eighth 

 day after copulation. When about to deposit its eggs the fly 

 alights on the substance which it selects as a suitable nidus 

 and, if possible, crawls down a crevice out of sight. There 

 it lays its eggs in clumps ; they are usually placed vertically 

 on their posterior ends and closely packed together. During 

 a single day, if undisturbed, a fly may lay the whole batch of 

 eggs which are mature in the ovaries and which may number, 

 I find from actual count, from 120 150. 



2. The Egg. The egg of M. domestica (PL 30, fig. 1) 

 measures 1 mm. in length, sometimes slightly less. It is 

 cylindrically oval ; one end, the posterior, is broader than the 

 other, towards which end the egg tapers off slightly. The 

 outer covering or chorion is pearly white in colour, the 

 polished surface being very finely sculptured with minute 

 hexagonal markings. Along the dorsal side of the egg are 

 two distinct curved rib-like thickenings having their concave 

 faces opposite. In the hatching of the eggs which I have 

 observed, the process was as follows : A minute split ap- 

 peared at the anterior end of the dorsal side to the outside of 

 one of the ribs ; this split was continued posteriorly (fig. 2), 

 aud the larva crawled out, the walls of the chorion collapsing 

 after its emergence. The time of hatching varies according 

 to the temperature. With a temperature of 25C. 35C. the 

 larvae hatch out from eight to twelve hours after the deposition 

 of the eggs ; at a temperature of 15C. 20C. it takes about 

 twenty-four hours, and if kept as low as 10C., two or three 

 days elapse before the larvae emerge. 



3. The Larva. First larval stage or first instar. 

 The newly-hatched larva (fig. 8), measures 2 mm. in length. 

 It contains the same number of segments as the mature larva 

 and at the anterior end of the ventral surface of each of the 

 posterior eight segments there is a spiny area (sp.). The 

 posterior end is obliquely truncate, and bears centrally the 

 only openings of the two longitudinal tracheal trunks, each 

 trunk opening to the exterior by a pair of small oblique slit- 



