XXXVITI 
ON THE METHODS AND SOURCES OF ERROR IN THE 
EXPERIMENTS ON ARTIFICIAL PARTHENOGENESIS' 
1. Because of various papers by European authors who 
have encountered difficulties in repeating or continuing my 
experiments on artificial parthenogenesis I wish to make a 
few remarks on the methods and the sources of error in 
these experiments. I do not need to dwell upon the impor- 
tance of sterilizing the sea-water, the instruments, the hands, 
and the animals themselves; it is self-evident. I wish 
in this connection to mention only the greatest sources of 
error, namely, the tendency of males, especially ripe sea- 
urchins, to fill the sea-water in the pail in which they are 
brought into the laboratory with sperm. It is therefore 
advisable to keep the females isolated for twenty-four hours 
or if possible even longer in sea-water free from sperm 
before using them in the experiments on artificial partheno- 
genesis. If one has taken the necessary precautions against 
infection with sperm, the next step is to bring the unfertil- 
ized eggs to development. In the eggs of sea-urchins the 
only effective method which is known thus far by which 
they can be made to develop parthenogenetically consists in 
keeping the eggs for about one and one-half hours in sea- 
water the osmotic pressure of which has been increased a 
definite amount. In general it is immaterial how this 
increase in osmotic pressure is brought about, whether 
through evaporation of the sea-water or through the addition 
of salt or sugar or urea to the sea-water. If we wish to 
obtain many and, as nearly as possible, normal larve, the 
choice of methods is somewhat more limited. I find after 
1 Archiv fiir Entwickelungsmechanik der Organismen, Vol. XIII (1902), p. 481. 
766 
Digitized by Microsoft® 
