96 Artificial Parthenogenesis 



unfertilized eggs of the sea urchin Arbacia to develop 

 into swimming larvas, blastulas, gastrulag, and plutei, 

 by treating them with hypertonic sea water of a definite 

 osmotic pressure for about two hours. When such 

 eggs were then put back into normal sea water many 

 segmented and a certain percentage developed into 

 perfectly normal larvae, blastulae, gastrulag, and plutei. T 

 Soon afterward this was accomplished by other methods 

 for the unfertilized eggs of a large number of marine 

 animals, such as starfish, molluscs, and annelids. None 

 of these eggs can develop under normal conditions 

 unless a spermatozoon enters. These experiments 

 furnished proof that the activating effect of the sper- 

 matozoon upon the egg can be replaced by a purely 

 physicochemical agency. 2 



The first method used in the production of larvae 

 from the unfertilized eggs did not lend itself to an 

 analysis of the activating effect of the spermatozoon 

 upon the egg, since nothing was known about the action 

 of a hypertonic solution, except that it withdraws 

 water from the egg; and there was no indication that 

 the entrance of the spermatozoon causes the egg to lose 

 water. No further progress was possible until another 

 method of artificial parthenogenesis was found. When 

 a spermatozoon enters the egg of a sea urchin or starfish 



1 Loeb. J., Am. Jour. Physiol., 1899, iii., 135; 1900, iii., 434. 

 ' Loeb, J., Artificial Parthenogenesis and Fertilization, Chicago, 1913. 

 The reader is referred to this bock for the literature on the subject. 



