ARTIFICIAL PARTHENOGENESIS IN ANNELIDS 655 



the two- to four-cell stages, but may in exceptional cases go 

 as far as the twelve- to sixteen-cell stages. We may say that 

 Chsetopterus possesses a higher degree of parthenogenetic 

 tendency than the Arbacia egg, which begins to segment 

 later, after about twenty hours, and does not proceed beyond 

 the two- to four-cell stage. 



2. The unfertilized eggs of Chsetopterus are able to 

 develop into swimming trochophores if they are put for about 

 one hour into one of the following solutions and then put 

 back into normal sea-water: 



(1) 15-20 c.c. 2n NaCl +85 c.c. sea- water 

 (2)40 2 n cane-sugar +60 " 



(3) 30 2n MgCl 2 +70 " 



(4) 10 5n CaCl 2 +90 



All these solutions have one element in common, namely, 

 the about equal increase of the osmotic pressure. It seems 

 therefore justifiable to assume that the increase in the 

 osmotic pressure or the loss of water on the part of the egg 

 is the cause of the parthenogenetic development of these 

 eggs. 



3. KC1 or perhaps the K ions seem to possess a specific 

 effect upon the eggs of Chsetopterus. We shall discuss this 

 fact more fully in the next section. 



Objections considered. The possible objection that the 

 eggs of Chsetopterus are naturally parthenogenetic in normal 

 sea-water or that spermatozoa had contaminated the sea- 

 water is rendered impossible through the behavior of the 

 control eggs and the antiseptic precautions taken. As far 

 as I can see, there is only one objection left, which, however, 

 although far-fetched and highly improbable, shall be consid- 

 ered. It might be argued that Chsetopterus is hermaphro- 

 ditic, but that the eggs and spermatozoa do not mature 

 simultaneously. This prevents fertilization of eggs in nor- 

 mal sea-water. But the increase in the osmotic pressure of 



