XXXVIII 



ON THE METHODS AND SOURCES OF ERROR IN THE 

 EXPERIMENTS ON ARTIFICIAL PARTHENOGENESIS 1 



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 Iarva3, the 

 choice of methods is somewhat more limited. I find after 



1 Archiv fiir Entwickelungsmechanik der Organismen, Vol. XIII (1902), p. 481. 



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