82 
Instead it now works upward, forming a curved tunnel, with smootii 
walls of well-packed earth webbed together by a thin coating of silk. 
(See PL XTII, fig. 1.) Normally the tunnel stops abruptly about one- 
eighth or one-fourth of an inch below the surface, leaving a thin wall 
of earth through which the moth must penetrate on emerging. As 
soon as the burrow has been completed, the larva repairs to the lower 
end (PI. XIII, fig. 1) and there transforms into the pupa, which lies in 
the cell, with the head slanting upward, until the emergence of the 
moth. A number of plaster casts of pupal burrows were made, and 
a few of them which show the typical variations in shape and size are 
figured on the accompanying plate (PI. XIII, fig. 2). 
VARIATIONS IN THE FORM OF THE PUPAL CELL. 
There is a very evident relation between the moisture content and 
cnaracter of the soil and the form of the pupal cell. In dry soil of a 
sandy nature the larvae always dig deeper than in moist soil of the 
same composition. (See fig. 8.) In the "black-waxy" soil of north 
Texas veiy shallow burrows were made, due no doubt to the mechan- 
ical difficulty ofi'ered by its tough consistency. In some cases the larvse 
could make no impression on dry, baked soil of this kind and were 
compelled to crawl into the cracks caused b}^ drying. 
In the accompanying table are given the dimensions of eight pupal 
cells made in moderately moist sandy loam. They were obtained by 
making plaster casts of the cells. These show a considerable individual 
variation. They average 46 mm. in depth and 43 mm. in horizontal 
extent. 
Table XXXI. — Dimensions of pupal cells. 
Vertical 
Horizontal 
extent. 
extent. 
Millimeters. 
Millimeters. 
53 
48 
71 
57 
80 
50 
38 
40 
26 
43 
20 
39 
57 
27 
20 
39 
Temperature also exerts an influence on the depth of the burrow. 
Larvae of the late fall brood dig much deeper than those pupating 
earlier in the season. In a lot of seven overwintered pupee, at Hetty, 
Tex., the depth of the respective cells in millimeters was as follows: 
50, 50, 125, 125, 125, 150, and 175, with an average of 114 mm. At 
Paris, Tex., six cells averaged 80 mm. in depth in black clay loam, 
and 13 in sandy loam averaged 98 mm., as compared with 46 mm. for 
the August brood. The reason for this is evident, since the over- 
wintering pupae must withstand many adverse conditions to which theil 
summer broods are not exposed. 
