IOWA ACADEMY OF SCIENCE 
221 
SOME OBSERVATIONS ON THE EMBRYOLOGY OF CHIRONOMUS. 
BY W. N. CRAVEN. 
A. INTRODUCTION TIME AND PLACE OF LAYING. 
All the eggs used in the following investigation were collected from a small 
pond in the eastern edge of the city of Indianola. The eggs were gathered 
from time to time at intervals of from one to three days, between June 20th 
and September 30th, 1902. They were found in abundance along the bank, in 
water from one to six inches deep. Usually they were attached to a piece of 
wood, or some plant growing in the edge of the water. Many were also found 
attached to the bottom. A few were found floating in the water, but as by 
far the greater number were attached, it is probable that those found floating 
had broken from their attachment, or by some accident had not been fastened. 
It w'as found that the eggs collected in the early morning were alwmys con- 
siderably advanced in their development; so that some of them must have been 
deposited the previous day. Those collected in the early afternoon were always 
at least in the early stages of development, while the most freshly laid eggs 
were collected about ten o’clock A. M. As the insects were always present 
about the edges of the pond in the early morning, it is probable that some little 
time, perhaps two or three hours, were consumed in depositing and fastening 
an egg mass. It is probable that the greater number were laid in the early 
morning — before ten A. M. As all the eggs in which the first stages of develop- 
ment had been reached were found about noon, by far the greater number must 
have been deposited in the early morning. 
B. THE EGG MASS. 
The eggs are laid in a clear jelly like mass, w^hich is about three-eighths of 
an inch in diameter and varying from one-fourth to three-fourths, or some- 
times nearly an inch in length. The egg mass was always attached by one 
end, and since its specific gravity is less than that of water, it assumes a nearly 
vertical position in the water. The eggs are arranged in the mass in the form 
of a spiral, which runs the length of the mass. The eggs are placed with 
their long axes in the line of the spiral, each egg lying slightly above and its 
end projecting over its predecessor. Hence in the normal position of the eggs 
in the water the embryo lies with its long axis nearly horizontal. ^ 
C. TIME OF INCUBATION. 
The time of incubation varied considerably for different egg-masses, although 
those of the same egg mass always hatched within two or three hours of the 
same time. 
