192 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



of Dendrostoma added, a certain percentage of the eggs formed a 

 typical fertilization membrane. On watching these eggs, it 

 was found that two to three hours after membrane formation 

 they formed a normal nuclear spindle and that some of them 

 divided quite regularly into two cells. In the majority, 'the 

 next division did not take place, but later they split up into 

 several cells at once. Normal appearing eight- and sixteen-cell 

 stages were very abundant, and I expected at first that the eggs 

 would develop into larvae; but this was not the case, with few 

 exceptions. On the second day, most of the eggs disintegrated. 

 A few lived a little longer, but did not develop into blastulae. 



If such eggs were placed immediately after membrane forma- 

 tion in hypertonic sea-water (50 c.c. of sea-water+8 c.c. 2J m 

 NaCl), all or most of the eggs developed into larvae. If the 

 length of exposure was correctly chosen the eggs segmented and 

 developed into plutei in quite a normal manner. If the expo- 

 sure was too short the hypertonic solution had no effect. 



It was not, however, the eggs of every sea-urchin that formed 

 membranes in Dendrostoma serum, the reaction being limited 

 to the eggs of about 20 per cent of the females. 



The next thing was to determine more closely the nature of 

 the active substance. If the reactions of the effective solution 

 of Dendrostoma blood are tested, it will be found that it reacts 

 to neutral red just like ordinary sea-water. This excludes the 

 possibility of membrane formation being due to one of the 

 lower fatty acids (or any other acid). For in order to cause 

 membrane formation by means of one of the lower fatty acids, 

 about 3 c.c. of N/10 acid must be added to 50 c.c. of sea-water, 

 and this renders the latter strongly acid. Moreover, the eggs 

 must not remain in this solution longer than 1 J to 2J minutes (at 

 15 C.), else no membrane is formed. In the third place, the 

 membrane is never formed in the acid sea-water (in the case of 

 the lower fatty acids), but only after the egg has been trans- 

 ferred to ordinary (i.e., faintly alkaline) sea-water. But when 



