ARTIFICIAL PARTHENOGENESIS IN ANNELIDS 679 



result may be due to the impossibility of the spermatozoon 

 of the one species entering the egg of the second species, or 

 to the fact that the spermatozoon of Chsetopterus brings 

 about the development of the Chsetopterus egg by substances 

 which are ineffective in the Arbacia egg, and vice versa, or 

 the spermatozoon of the one species is poisonous for the egg 

 of the other species, or vice versa. 1 The second possibility 

 is of interest to us on account of the fact that we can bring 

 about the parthenogenetic development of the Chsetopterus 

 eggs by means which have no effect upon the Arbacia egg. 

 When we intend to produce artificial parthenogenesis in 

 the eggs of Echinoderms, it is only necessary to put them for 

 from one and one-half to two hours in sea-water, the osmotic 

 pressure of which has been raised about 37^ to 75 per cent. ; 

 that is, into sea- water to which has been added 12^ to 25 per 

 cent, of its volume of a 2^n NaCl solution or of a solution 

 isosmotic with the latter. We have not yet determined the 

 osmotic pressure of the sea-water at Woods Hole, and on 

 indirect data assume that it is about isosmotic with a ftw 



o 



NaCl solution. The optimal increase of osmotic pressure 

 varies for different species and even for different females of 

 the same species. It may be that the temperature of the 

 water and the degree of maturity of the eggs play a r6le. 

 In making experiments of this kind, it is necessary to use 

 always a series of solutions of different osmotic pressure and 

 to take the eggs out at various intervals, from one-half to two 

 hours or more, until the optimum concentration and time 

 have been ascertained. 



An increase in the osmotic pressure of the sea-water is 

 also able to cause artificial parthenogenesis in Chsetopterus. 

 The chief difference between the Chsetopterus and Arbacia 

 eggs is that at the same temperature the Chsetopterus eggs 



1 Certain constituents of the blood (globulins, enzymes?) frequently destroy the 

 blood corpuscles of other species that are not closely related. 



