XXVI 



ARTIFICIAL PARTHENOGENESIS IN THE EGGS OF 

 ANNELIDS 



1. The eggs of the annelids which we shall consider here 

 differ from the eggs of both sea-urchin and starfish in that 

 the spermatozoon enters the immature egg and thus sets in 

 motion the giving-off of the polar bodies as well as the develop- 

 ment of the egg. In the case of the starfish the spermatozoon 

 must enter immediately after the maturation division has 

 begun or is completed; in the case of the sea-urchin the egg 

 can remain for some time in a resting condition after the polar 

 bodies have been given off. 



We shall first consider the phenomena of fertilization in 

 Polynoe, an annelid of the Pacific coast. When the eggs are 

 taken out from the animal they are irregular in outline and 

 are surrounded by a thick chorion. The large nucleus is 

 plainly visible. When the unfertilized eggs are put into sea- 

 water (which contains no sperm) the chorion is dissolved in the 

 sea-water after the lapse of several hours, and the egg then 

 becomes spherical and black. Maturation does not, however, 

 proceed farther if the egg remains in sea-water. I put the 

 eggs of Polynoe into sea-water and left them there for between 

 two and four hours at 15° C, until they had become round. 

 They were then placed in a watch glass with 4 c.c. of sea- 

 water to which had been added 15' drops of a very weak solu- 

 tion of saponin in sea-water. Now the eggs which had been 

 treated with saponin for one minute, and then washed, formed 

 a beautiful fertilization membrane and began to extrude their 

 polar bodies in from five to thirty minutes. Some of the eggs 

 developed into swimming larvae in the course of from eighteen 

 to twenty-four hours, in most cases without undergoing 



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