414 Annals Entomological Society of America [Vol. V,. 
filter but at some depth since larve, pupz, and adults were 
found two feet below the surface and it was evident that the 
adults encounter no difficulty in traversing the interstices. 
The eggs are oval in shape and the majority show a slight concavity 
on one side accompanied by a corresponding convexity on the other, 
thus giving the eggs the appearance of being slightly bent in one plane. 
Sometimes this concavity is so reduced that this aspect of the egg is. 
almost straight. A large number of eggs were measured, and it was 
found that they are quite constant in size. The length varied only from 
0.32 mm. to 0.34 mm.,'and the measurements of the greatest diameter 
showed a variation of only 0.09 to 0.1 mm. The yolk is centrally 
located and comprises about one-half of the bulk of the egg. It is opaque, 
granular, and shows a homogeneous distribution in the freshly deposited 
egg. The substance outside the yolk is transparent and homogeneous. 
This substance is largely confined to the ends of the egg, and one end 
usually containing a larger quantity than the other. The outer egg 
membrane is smooth and transparent. 
Development proceeds rather rapidly and in about sixteen 
hours after oviposition most of the eggs are in an advanced 
stage of development. Not all of the eggs of a given mass. 
develop at the same rate, but some lag behind and therefore 
hatch later. The time between the laying and the hatching of 
the eggs was found to vary from about thirty-four to forty- 
eight hours. 
THE LARVA. 
(Fig. 6, Pl. XXXII.) 
Larve in all stages of development occurred in great abund- 
ance in the sprinkling filter beds. The influents of these filters. 
come from the settling and septic tanks and are thrown out. 
into the air in a spray which falls on the surface of the filter bed 
and filters through about ten feet of crushed limestone. This- 
influent carried considerable solid organic matter in suspension, 
some of which is retained in the filter. This sludge accumu- 
lates in some quantity on the surfaces of the stones and in the 
interstices formed by them, particularly in the upper part of 
the bed. The larve are found crawling through and over 
this sludge, and no doubt derive their food from it. Often larve 
may be found completely buried in the sludge with only the 
posterior breathing tube projecting into the air. They are 
active in their habits, and their characteristic crawling and 
wriggling form of locomotion is moderately efficient. They 
crawl with comparative ease over the surface of the filter rocks- 
and even have the ability to crawl up the side of a glass vessel 
in which they may be confined. 
