ARTIFICIAL PARTHENOGENESIS IN ANNELIDS 647 
ments, it is extremely hard to avoid an infection of the eggs 
by sperm. I proceeded as follows in the experiments with 
Chetopterus. As soon as the animals were brought into the 
laboratory by the collector, the tubes in which they live were 
opened and the worms removed. As soon as the first female 
was found it was put into a special dish and thoroughly 
washed off with sea-water, the water being renewed from six 
to twelve times in succession. The sea-water in the labora- 
tory was found to be absolutely free from spermatozoa of 
Chetopterus. (The animals are found on the beach of an 
island at some distance from the laboratory.) After the 
female had undergone the process of washing, it was exposed 
to a current of sea-water over night to remove as far as pos- 
sible any spermatozoa that might have been left on the sur- 
face. The next day the animal was ready to be used for an 
experiment. On that day and before the experiment began, 
the experimenter did not bring his hands in contact with 
any other Chetopterus or with the aquarium that contained 
such animals. His hands and instruments were sterilized 
with fresh water. The posterior part of the animal which 
contains the eggs was cut off and thoroughly washed for two 
minutes in distilled or fresh water. Had any spermatozoon 
been left on the surface of the animal, the distilled water 
would have killed it. After this the part containing the eggs 
was put into a vessel with sterilized sea-water, washed off 
once more and then put into another dish containing steril- 
ized sea-water. In this dish the single parapodia were 
opened successively, the eggs sucked out from each with a 
pipette, and then collected in another dish with sterilized 
sea-water. After all the eggs had been collected they were 
divided into two lots. The one lot remained in normal 
(sterilized) sea-water, to serve as control material. The 
other lot was distributed into the various solutions whose effect 
T intended to test. In no case did I see a single egg of the 
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