132 THE BLOWFLIES oF NortH AMERICA 
dry tissues and rarely on moist surfaces. The ege mass con- 
sists of from 10 to 393 eggs and is oval, shinglelike, and usually 
tightly glued to the surface of the wound, although it may not 
have the characteristic flat shinglelike appearance when attach- 
ed to wool or hair near a wound. 
Individual eggs (pl. 33, F and G) are approximately 1.04 
mm. in length and 0.22 mm. in diameter; reticulated, glistening 
white or slightly tinged with cream color, rounded posteriorly, 
somewhat flattened anteriorly, with a dorsal ridge or seam ex- 
tending from anterior end almost to posterior end, dividing at 
anterior end and extending ventrally around micropyle in a 
broad band, giving the appearance of a circular cap. 
Under natural conditions the duration of the ineubation 
period ranges from 11 to about 21 hours. Eggs deposited on 
wounds probably are subjected to a more or less constant tem- 
perature. It has been observed that eggs of americana which were 
exposed to temperatures near 30° F’. were killed. _ 
Larva'. First-instar: Elongate, more or less cylindrie in 
shape, with 12 apparent segments, tapering anteriorly from 
sixth segment; the last three segments slightly tapering posteri- 
orly; length and width at time of hatching 1.2 mm. and 0.23 
mm., respectively; fully developed first-instar larvae an aver- 
age of 3.6 mm. in length and 0.57 mm. in width at widest point. 
Armed with large dark single-pointed recurved spines arranged 
in more or less irregular rows near margin of segments; spines 
in anterior rows largest, larger spines measuring approximately. 
20 microns in length. Segments 2 to 9 each completely encircled 
with a band of spines at anterior margin; segment 11 without 
spines on dorsum, laterally reduced to two or three rows of 
small, more lightly pigmented spines; segment 12 with spines 
confined to ventral and ventrolateral surfaces; segments 6 to 12 
ventrally each with the band of spines wider and transversely 
divided by a narrowed spineless area; each segment posteriorly 
devoid of spines except for two or three rows of small spines on 
ventral surface of each of segments 5 to 12; segments 5 to 10 lat- 
erally each with fusiform areas which are provided with a group 
of spines. Twelfth segment depressed behind, with the two pos- 
terior spiracles located dorsally in the depression; each spiracle 
comprised of two small broadly oval apertures, each of which 
is encircled by a delicately sclerotized ring, from which finger- 
like projections extend toward the’center of the opening; fre- 
quently the two openings are so closely joined at the inner ven- 
‘This description, modified, is that by Knipling (Laake et al, 1936, pp. 
5-12). 
