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sperm. All eggs developed with great regularity, beginning to segment 

 about one hour after fertilization. 



Second experiment. Similar eggs not fertilized; not a single egg 

 developed. 



Third experiment. Similar eggs fertilized by Arbacia sperm. None 

 of the eggs showed any trace of cleavage until two to three hours after 

 fertilization. Then a small percentage segmented, a few regularly, 

 others irregularly. After four or five hours a large number of the 

 unsegmented eggs were Polyspermie. From this third lot quite a 

 number of blastulae and gastrulae were obtained. These will be de- 

 scribed below. 



Fourth experiment. Similar eggs, shaken, fertilized with Arbacia 

 sperm. Same result as in the third experiment. 



Fifth experiment. Similar eggs, shaken, but not fertilized; 

 not a single egg developed. The five experiments speak for themselves ! 



The embryos obtained by fertilizing the Asterias eggs with the 

 Arbacia spermatozoa differed from the normal Asterias embryos. The 

 eggs themselves did not begin to segment until an hour later than 

 the normal eggs, which were in the eight and sixteen cell stages when 

 the crossed eggs began to segment. The blastulae were much smaller 

 than the normal Asterias blastulae. The walls of the blastulae were 

 much thicker than in the Asterias larvae. A strongly marked polar 

 difference was found, due to thicker cells at one pole. Most of the 

 embryos gastrulated but died after forty-eight hours. 



I see only one possible source of error in the experiment. The 

 spermatozoa of Arbacia were obtained by squeezing the male and 

 washing off in sterilized water the sperm as it came out. It is con- 

 ceivable that Asterias spermatozoa might have been sticking to the 

 test of the Arbacia. The source of error is small and would not 

 account for the large number of spermatozoa necessary to fertilize so 

 many eggs. At most but a few drops of unsterilized water could have 

 gotten in, and even a liter of such water is found to contain very few 

 spermatozoa. The eggs we saw began to segment an hour or two 

 after the normal eggs. This Heetwig has shown to be a characteristic 

 phenomenon in eggs of one genus of sea-urchin fertilized by spermatozoa 

 from a different genus. The blastulae were different from the normal 

 Asterias blastulae. The Polyspermie eggs show that Arbacia sperm- 

 atozoa can enter Asterias eggs. 



We may safely, I believe, draw from these data the conclusion 

 that in [-, the experiment we have succeeded in fertilizing the eggs of 



