156 THE BLOWFLIES oF NortH AMERICA 
erately cool weather is apparently favorable for development, 
but the larvae will not mature under continued low tempera- 
tures. 
First instar?: Length 2.5-3.9 mm. Complete spinose bands on 
each of segments 2 to 9; segment 10 without or with only a few 
spines on dorsum, on segments 11 and 12 these restricted to ven- 
tral or ventrolateral surfaces; spines on posterior margin of seg- 
ments restricted to a single row each on venter of segments 7 
to 12. All spines light to dark brown, each with a single point, 
the larger spines 6 microns in length. Three small tubercles 
above and three small ones below posterior cavity. Posterior 
spiracles each with two slits appearing confluent below and not 
surrounded by peritreme. Amphipneustic. Cephaloskeleton 
(pl. 36, B) as illustrated. 
Second instar: Length 4.0-9.5 mm. Spinose bands and dis- 
tribution of spines essentially as in previous instar, but each 
spine with one to three points, usually with two; a V-shaped 
group of spines located on anal protuberance similar to that in 
Callitroga macellaria. Tubereles located as in previous instar. 
Posterior spiracles each with two slits surrounded by incomplete 
peritreme. Anterior spiracles each with about 12 branches. 
Cephaloskeleton (pl. 36, C) as illustrated. 
Third instar: Mature larva (pl. 36, A) 8.5-17.0 mm. in length. 
Segments 2 to 9 each provided with complete spinose bands at 
anterior margin; segment 10 with band incomplete on dorsum; 
segment 11 with band generally restricted to ventral and ventro- 
lateral surfaces; posterior margin of all segments without spines 
on dorsum. Anterior spiracles with about 12 branches each. 
Posterior spiracles (pl. 36, E) relatively large and provided with 
a broad peritreme, the greatest diameter of one spiracle av- 
eraging 0.387 mm.; tubercles three on upper, and three on lower, 
margin of posterior cavity; inner and outer pairs on upper mar- 
gin approximately equal in size, the median pair somewhat 
smaller; inner pair separated by less than two-thirds the distance 
between inner and outer tubercles on each side; outer tubercles 
on lower margin larger than median, and inner tubercle greatly 
reduced. Anal area (pl. 36, F) with two prominent tubercles, the 
spines of which are arranged in a V-shaped group. Cephalo- 
skeleton (pl. 36, D) approximately 1.6 mm. in length, resembling 
that found in Cochhomyia but possessing an accessory oral 
selerite not found in closely related genera. 
Prepupa. This stage is 3 to 7 days in duration at a mean air 
*Adapted from Deonier and Knipling (1940). Many of the biological 
notes on wheelert were abstracted from this paper. 
