144 Tur BLOWFLIES OF NortH AMERICA 
tures much below this; less than a 10 percent hatch occurred at 
59° F. At 104° F. incubation was completed in 6.73 hours, but 
no hatch was obtained at 109° F. The optimum temperature for 
the hatching of eggs of this species appears to be at about 89° F., 
.at which temperature it requires 8.13 hours to complete ineuba- 
tion. 
Larva.* First instar: Size and general form similar to those — 
of americana. Spines small and brownish in color, all spines with 
a single point, the larger spines approximately 6 microns in 
length. Last segment slightly depressed behind. Posterior 
spiracles similar to those of americana. Tubercles bordering pos- 
terior cavity poorly defined. Cephaloskeleton (pl. 35, A) dif- 
fering significantly from that of americana, the pharyngeal 
sclerites each with a prominent anterodorsal projection and join- 
ed at anterior extremity, the parastomal sclerite broader and the 
labial sclerites greatly different in structure, these consisting of 
a pair of irregular elongate sclerites with a large number of 
small hooklets closely grouped at anterior extremity; the cephal- 
oskeleton considerably larger than in americana, the length rang- 
ing from 0.33—0.34 mm. (average of 10, 0.836 mm.; average 
width at widest point, 0.125 mm.). 
Second instar: Shghtly less robust than in americana. Spines 
small, length of larger spines approximately 20 microns; spines 
in anterior rows of each band generally with two and oceasionally 
with three points, those in posterior portion of band more often 
with one point. Anterior margins of each of segments 2 to 9 
completely encircled with spines, segment 10 with band inter- 
rupted on dorsum and segments 11 and 12 with spines restricted 
to ventral and ventrolateral regions; dorsal and lateral spines 
wanting posteriorly on margins of all segments, while in ameri- 
cana the posterior margins of segments 11 and 10 are armed with 
several lateral and dorsal rows of spines. Anterior spiracles. 
more often with 9 or 10 branches. Posterior spiracles (pl. 35, C) 
more lightly pigmented and smaller than those of americana 
(average greatest diameter approximately 0.12 mm.); tracheal 
trunks leading from posterior spiracles not pigmented. Tuber- 
cles on border of posterior cavity larger and more conspicuous 
than in americana, the general appearance of last segment es- 
sentially as in third instar. Cephaloskeleton (pl. 35, B) with 
labial sclerites comparatively short and not so broadly eurved 
as in americana; length of cephaloskeleton from 0.73-0.80 mm., 
average width approximately 0.38 mm. 
*This description is a modification of Knipling’s, in Laake et al. (1936, 
pp. 12-18). 
