50 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



When in the spring of 1887 my brother and I performed experi- 

 ments upon the fertilization of sea-urchin eggs, we had before us the 

 question as to what influence the concentration of sperm exerted upon 

 the polyspermous fertilization of injured eggs, and especially those 

 whose life functions had been interfered with through treatment with 

 reagents. Thus eggs were treated for thirty minutes with a 1 per cent 

 solution of strychnin and then mixed with sperm of the same species 

 at various dilutions. In one case the sperm was so much diluted with 

 sea- water that on the evidence both of observation in the living con- 

 dition and of a very thorough examination of preserved material more 

 than 90 per cent remained unfertilized owing to the addition of insuffi- 

 cient sperm. Fifty minutes after fertilization the control material 

 was preserved. As before, 89 per cent of them were unfertilized. In 

 these I found the beginning of an interesting change, which I will 

 here describe. 



Briefly, this alteration consisted in the fact that the nucleus 

 showed changes similar to those occurring after fertilization. 

 The division processes started in the nucleus, but, "in the 

 majority of cases a nuclear or cell division did not take place. 

 In exceptional cases a single division of the egg into two cells 

 occurred, and each of these was provided with a nucleus. These 

 cases which approach nearest to a normal division process are 

 rare, and they also differ from the normal'' (p. 44). Later 

 Hertwig convinced himself that the longer sea-urchin eggs had 

 lain in sea-water without the addition of sperm, the more of 

 such divisions incidentally occurred. We shall later return to 

 this phenomenon. 



In 1892 the writer 1 found that if the freshly fertilized eggs 

 of a sea-urchin (Arbada) are brought into hypertonic sea-water 

 (about 100 c.c. of sea-water+2 g. NaCl) the eggs do not divide 

 in such a solution; but if they are returned to normal sea-water 

 after two, three, or four hours, in quite a short time, after twenty 

 or even ten minutes, the egg breaks up into several cells at 

 once; and indeed the longer the eggs remain in the hyper- 

 tonic solution, the greater the number of the cells into which 



1 Loeb, "Experiments on Cleavage," Jour. Morphol., VII, 253, 1892. 



