CH. x] METHODS 141 



raising of the osmotic pressure of the water. One method, 

 therefore, bringing about artificial parthenogenesis is by 

 the action of hypertonic solutions. It was then found that 

 acids and alkalis were also effective; in some cases causing 

 only the beginning of development, which was often irreg- 

 ular, but in others bringing about normal segmentation 

 followed by development into typical larvae. In the earlier 

 experiments segmentation took place without the formation 

 of a "fertilisation membrane" and the larvae produced 

 were weakly and failed to develop to the later stages. 

 Further experiment, however, proved that it was possible 

 to induce the formation of a typical fertilisation membrane, 

 and that by suitable treatment all the eggs could be caused 

 to develop into quite strong healthy larvae. LOEB'S im- 

 proved method for bringing about artificial partheno- 

 genesis of Sea-urchin eggs is to treat them first with butyric 

 acid (2-8 c.c. N/io butyric acid to 50 c.c. sea-water). Other 

 acids, especially organic acids of the fatty series, are effective 

 but butyric is found to be most suitable. After treatment 

 for a few minutes (at 15 C.) with butyric acid the eggs are 

 transferred to pure sea-water, and then after 15 to 30 

 minutes to a hypertonic solution consisting of 50 c.c. sea- 

 water to which 8 c.c. ai m. sodium chloride has been added. 

 After half-an-hour in the hypertonic sea-water batches of 

 eggs are transferred during the next half hour at five 

 minute intervals to pure sea-water, when the eggs that have 

 been treated for the correct time begin to segment normally. 

 Different species of urchin, and the same eggs under different 

 conditions of temperature or other circumstances, require 

 somewhat different lengths of exposure to the solutions. 

 The treatment with hypertonic sea-water may precede that 

 with butyric acid instead of following it, but in this case the 

 exposure must be about twice as long. 



