Tuer Brotocy oF EPHYDRA SUBOPACA LOEW 581 
the salivary glands are relatively large. This stage lasts from four to 
five days at a room temperature of from 23° to 35° C. 
The second instar.— At this time the larva is provided with a pair of 
pale, slender, anterior spiracular processes, the digits of which are short 
and not distinct. The posterior spiracles have assumed the general shape 
that they will have in a full-grown larva, but are smaller in size. Each 
of them has a chitinous cap with an opening at the center, surrounding 
which are four tubercles. The cephalopharyngeal skeleton is much 
thicker and heavier than in the preceding stage, and the hypostomal 
sclerite is now a separate piece from the lateral pharyngeal plate. This 
stage lasts about four days at a temperature of from 25° to 28° C. 
The third instar.— The larva has attained its maximum size of from 
12 to 13 millimeters in length. The difference in body structure has 
been described under Morphology, page 567. The larva completes its 
development and pupates in the course of three or four days at a temper- 
ature of from 29° to 30° C. Sometimes under less favorable conditions 
this stage may extend over a period of about a week. 
Observations on growth in salt and fresh water 
The following experiments were performed in the laboratory. Each 
aquarium was 5.5 centimeters in diameter and contained water, salt and 
fresh, with a depth of about 1.25 centimeters. Water and food materials 
were added whenever necessary. The aquaria were in series, placed near 
a window and carefully guarded against dirt and accident. 
Experiment I.— Three larvae, each of which measured from 2 to 2.5 
millimeters in length, were placed in salt water. After four days they 
measured 5 millimeters each; after five days one of them measured about 
7 millimeters and the other two about 6 millimeters; after seven days 
the largest one measured 9 millimeters; after eleven days the largest 
larva pupated, while the other two measured 9 and 7 millimeters, respec- 
tively; two days later the remaining two larvae pupated. The room tem- 
perature ranged from 23° to 29° C. 
Experiment II.— Three larvae of the same size as those used in Experi- 
ment I were placed in fresh water. After four days each one measured 
about 4 millimeters; after five days they averaged from 4.5 to 5.5 milli- 
meters in length; after seven days one measured 7 millimeters and died, 
while the other two measured about 6.5 millimeters on the tenth day 
