222 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



Naples by treating their eggs with hypertonic sea-water. 1 

 He also investigated the effect of acids. 



Hydrochloric acid has been found by Loeb to be an efficient 

 reagent for causing artificial parthenogenesis in starfish. He found it 

 did not succeed in Arbacia punctulata (at Woods Hole). But strangely 

 enough it is one of the best reagents I found for Arbacia pustulata 

 (at Naples). Usually 2, 3, 4, 5, 6, and 7 c.c. of a N/10 solution of 

 hydrochloric acid in sea-water was added respectively to dishes 

 containing 100 c.c. of sea-water. Eggs immersed in these solutions 

 were taken out at intervals of from two to fifteen minutes. Some of the 

 best results were obtained from 2 c.c. acid in 100 c.c. sea-water, ten to 

 fifteen minutes' exposure; 3 c.c. acid, seven to twelve minutes' 

 exposure; 4 c.c. acid, nine minutes' exposure; 7 c.c. acid, five minutes' 



exposure In the best experiments perhaps 10 per cent of the 



eggs developed into swimming larvae. Many of these swam up to 

 the top of the liquid, just like the larvae from fertilized eggs. They 

 formed fully developed plutei which lived as long as individuals pro- 

 duced from fertilized eggs and kept under the same conditions. 



No positive results were, however, obtained by this method 

 at Naples with S. lividus, but Lyon succeeded in obtaining a 

 couple of larvae by treating the unfertilized eggs of S. lividus 

 with carbonic acid in sea-water. The importance of membrane 

 formation from the point of view of development was not recog- 

 nized at that time, but I believe that the eggs in Lyon's experi- 

 ment formed a gelatinous membrane. 



We may as well point out here that the eggs of S. purpuratus 

 and franciscanus at Pacific Grove cannot be made to develop 

 into larvae by a mere treatment with acid unless they are kept 

 at a very low temperature. In this respect, there is a quali- 

 tative difference between the eggs of the European and Cali- 

 fornian sea-urchins. 



This difference between the behavior of the eggs of 

 Strong ylocentrotus at Naples and in California is also corrobo- 



1 E. P. Lyon, "Experiments in Artificial Parthenogenesis," Am. Jour. 

 Physiol., IX, 308, 1903. 



