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. Onthe 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. 23 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 e.c. of sea-water, 
and this renders the latter strongly acid. Moreover, the eggs 
must not remain in this solution longer than 13 to 23 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 
