258 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
segmentation; a few segmented into two or four cells, but not 
farther. One often saw eggs that had remained stationary in 
the two-cell stage, swimming about as larvae, although they 
always consisted of merely the two cells. The eggs developed 
very slowly into larvae in the course of from eighteen to 
twenty-four hours.  Fertilized eggs reached the trochophore 
stage in eight hours at the same temperature.! These experi- 
ments in which the eggs of Polynoe are made to develop by 
merely producing membrane formation by means of saponin 
(or solanin) are not invariably successful, and the number of 
developing larvae was often very small. But they indicate 
that the development of the egg depends upon the same 
conditions as in the sea-urchin egg, namely upon membrane 
formation. 
It was next tried whether or not development could be made 
more normal by exposing the eggs to hypertonic sea-water 
after membrane formation. This proved to be the case. 
Immature eggs freshly taken from the animal were subjected 
to treatment with saponin. Two drops of a very weak solution 
of saponin were added to 5c.c. of sea-water, and after four 
minutes the eggs were transferred to ordinary sea-water and 
freed from saponin by being washed four times. The eggs did 
not form a membrane in the saponin solution, but the chorion 
was dissolved, and the eggs rounded off. They were then put 
into hypertonic sea-water (50 c¢.c. of sea-water+8 c.c. 25 m 
NaCl), and portions of the eggs were replaced in ordinary sea- 
water, after exposures of 60, 104, 140, 162, and 180 minutes 
respectively. All the eggs formed fertilization membranes 
in the hypertonic solution; this was a secondary effect of the 
exposure to saponin. However, the eggs placed in sea-water as 
a control also formed a membrane there. 
The control eggs, and those exposed to the hypertonic 
sea-water after the saponin treatment for only one hour, did 
‘Loeb, ‘‘Ueber die Entwicklungserregung unbefruchteter Annelideneier 
(Polynoe) mittels Saponin und Solanin,” Pfliiger’s Archiv, CX XII, 448, 1908. 
