ARTIFICIAL PARTHENOGENESIS IN ANNELIDS 259 



not divide, and did not in this experiment develop into larvae. 

 On the other hand, practically all of the eggs treated with 

 saponin that had been two hours and twenty minutes in the 

 hypertonic sea-water segmented, but reached only the eight-cell 

 stage in four hours after removal from the hypertonic sea-water. 

 Four hours later these eggs had reached the trochophore stage 

 and were swimming about. But it is doubtful whether they 

 had undergone any further segmentation. Eggs that had been 

 exposed only to hypertonic sea-water, without previous mem- 

 brane formation under the influence of saponin, did not develop 

 into larvae. This experiment was repeated, and it was then 

 found that, though by producing membrane formation by 

 means of saponin a few eggs of Polynoe can indeed be made to 

 develop into larvae, a subsequent exposure to hypertonic sea- 

 water causes many more eggs to develop. The rate of develop- 

 ment is also increased by this method. The analogy in behavior 

 between the eggs of Polynoe and of the sea-urchin is obvious, 

 although not complete, since the sea-urchin eggs all develop 

 in this case by segmentation, while the eggs of Polynoe develop 

 without or only with incomplete segmentation. 



The eggs of Polynoe resemble the eggs of the starfish, in 

 so far as the membrane formation suffices for the causation of 

 development of some eggs, and in so far as the addition of the 

 second corrective factor increases the number of eggs capable 

 of development. 



2. There is yet another method by which the unfertilized 

 eggs of Polynoe can be made to develop. This is by raising the 

 alkalinity of the sea-water. 1 



If the concentration of the hydroxy lions in sea-water be 

 raised by the addition of a considerable amount of sodium 

 hydrate, not only can the unfertilized eggs of Polynoe be induced 

 to ripen, but a small percentage of them will segment into two 

 or four cells; and sometimes a large percentage or even all the 



1 Loeb, "Ueber die allgemeinen Methoden der kunstlichen Parthenogenese," 

 Pfluger's Archiv, CXVIII, 572, 1907. 



