ARTIFICIAL PARTHENOGENESIS IN ANNELIDS 651 



1 and 2 developed into trochophores, very few of the eggs of 

 solution 4 and none of solution 3 reached the trochophore 

 stage. The control eggs remained undeveloped. 



Fourth series. The results were obviously puzzling if 

 the increase of the osmotic pressure was the only factor that 

 brought about the development of the unfertilized eggs of 

 Chsetopterus. But they would be intelligible if there were, 

 in addition to the effect of an increase in the osmotic pres- 

 sure, a specific effect of the KC1 or the K ions. In order 

 to decide this, the unfertilized eggs of a female were dis- 

 tributed into the following solutions: 



(1) 5 c.c. 1\n KC1 +95 c.c. sea-water 



(2) 10 " " +90 



(3) 15 " " +85 " 



(4) 5 " NaCl + 95 " 



(5) 10 " +90 " 



(6) 15 " " +85 " 



(7) Normal sea-water (control) 



The eggs remained one hour in these solutions. 



The next day the control eggs (7) were undeveloped. 

 The eggs that had been in the first three solutions were 

 teeming with trochophores. In lots 4 and 5 not a single 

 swimming trochophore was found, although many eggs had 

 begun to develop. The development stopped, however, in 

 an early stage. Of the eggs that had been in solution 6 a 

 large number had reached the trochophore stage and were 

 swimming. These results were as clear as could be desired. 

 In order to bring about artificial parthenogenesis through 

 the addition of NaCl, 15 c.c. of the 2^n solution had to be 

 added, while 5 c.c. of a 2^n KC1 solution were sufficient. 



Fifth series. There was a possibility that the effect pro- 

 duced by NaCl was a specific Na effect, and not an effect of 

 the increase in osmotic pressure. An experiment with cane- 

 sugar could decide this question. My stock solution of 



