No. 420.] HISTORY OF STICHOSTEMMA. IOOI 
probably indicating their later origin in the species. I have 
not been able to ascertàin whether the food of the young 
is the same as that of the adult. 
THE BREEDING SEASON AND ITS RELATION TO THE 
ENVIRONMENT, 
The breeding season of Stichostemma extends from May to 
November or December, according to the temperature of the 
water. Practically every specimen taken soon after the ice 
melts in the spring contains the growing oócytes in the gonads, 
and these reach their full size, and egg-laying begins as soon as 
the shallow water along the shores becomes sufficiently warm. 
During the whole of the season from May to November the 
very young worms are abundant in sizes, varying from a milli- 
meter up, and the eggs are often found in the alge with the 
worms. 
Egg-laying occurs freely in the laboratory. Often when the 
algze containing worms are brought in and allowed to stand for 
twenty-four hours, a large number of egg strings will be found 
near the surface and on the sides of the jar. Apparently the 
eggs are always laid during the night or in darkness when the 
animals are moving about freely. Even in jars of clear water 
and without food the eggs are often deposited abundantly dur- 
ing the first few days of captivity, but individuals which do not 
lay eggs during that time are not likely to do so later, though, 
as experiment shows, they contain fully grown oocytes. 
Eggs can be obtained in the laboratory at any time during 
the year when the worms can be found in moderate numbers. 
During December many individuals with oócytes at least half 
grown are found. In nature these eggs are probably not laid 
until the following spring, but if the worms are kept at room 
temperature in the laboratory a number will usually deposit 
eggs within a week or two, and this will occur even if the 
animals are kept without food. By these observations and 
those made upon animals under natural conditions during 
nearly two years, I am convinced that the limits of the breed- 
ing season are determined chiefly by the temperature of the 
