TRANSFORMATIONS OF BUFFALO GNATS. 25 
DESCRIPTION OF PUPA OF SIMULIUM BEACTEATUM. 
The pupa of 8. bracteatum (PI. IV, fig. 3) measures about 4 mm. in length and 
is of a golden yellow color when first formed. 
The respiratory filaments are composed of a single main trunk on either 
side of the thorax, each of which divides in the following manner: Two long 
branches arise from the base of the main trunk, which again divides a short dis- 
tance farther up, making four long branches on each side, counting the 
branches at the distal ends. The hooks on the abdomen are arranged as usual. 
The pupae were reared from larvae and determined from adults 
reared from them and compared with the type. 
DURATION OF PUPAL STAGE. 
The duration of the pupal stage of S. venustum, according to 
Mrs. Sarah J. McBride, at Mumford, N. Y., is three weeks. The 
maximum period in the pupal stage of the same species observed by 
the writer was nine days at Havana, 111., late in the fall, the average 
temperature during that period being 36° F. 
The minimum period in the pupal stage of S. venustum was a little 
over 84 hours at Spartanburg, S. C, during the month of June, with 
a temperature from 70° to 90° F. The average length of the pupal 
period for the five species under consideration, during the summer, 
is from five to seven days. 
The general effect of low temperature seems to be to retard, and 
of rising temperature up to 90° F. to hasten the emergence of the 
adult from the pupa. The effect that low air temperature has on the 
pupa in retarding development is much less in proportion than the 
effect that a rising temperature between 60° and 80° F. has in 
hastening emergence. Though their structure is normally adapted 
for aquatic life, yet when they are exposed to the air, as sometimes 
happens when the water falls, they will often emerge even after 24 
hours spent out of water if the adult is sufficiently developed within 
the pupal skin. This was especially noticeable at Havana, 111., in 
1912, when the river began to fall. 
The respiratory system of the pupa is a modification of the general 
tracheal system of the larva. The rectal gills having been cast off, their 
function appears to be assumed by the tubelike filaments arising on each 
side of the thorax. There are two long main trunks extending down 
each side of the abdomen. These give off branch tracheae, connected 
by commissures, which lead to the abdominal spiracular chambers, 
from which arise the initial threads leading to the spiracles. The 
spiracles are cuticular invaginations and become closed, according to 
Taylor, 1 on the withdrawal of the old tracheae at the time of the 
1 Taylor, T. H. On the tracheal system of Simulium. In Trans. Ent. Soc. London, 1 
1902, p. 701-716 (p. 703), 8 fig., 1902. 
