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 nQxt 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 5 c.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. 2| 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 



1 Loeb, "Ueber die Eutwicklungserregung unbelruchteter Anaelideneier 

 (Polynoe) mittels Saponin und Solanin," Pfiuger's Archiv, CXXII, 448, 1908. 



