14 PROBLEMS OF FERTILIZATION 



period broke suddenly. In 1873 Biitschli observed in 

 the egg of a nematode the approach and contact of the 

 two structures, which we now know to be the germ nuclei, 

 immediately preceding the first cleavage of the ovum. 

 But no interpretation was presented. In 1874 Auer- 

 bach described the appearance of two nuclei at opposite 

 ends of the elongated egg of Rhabdites; these increase 

 in size, migrate toward the center of the egg, meet, 

 rotate through 90°, and fuse together. A dicentric 

 figure appears and cleavage follows. What is the origin 

 of these two nuclei and the significance of their union ? 

 The fusion of two nuclei was at the time entirely without 

 analogy. Auerbach states: ''It is natural to assume 

 that, as for the reproduction of organisms the copulation 

 of two individuals, or at least of two cells in some form 

 or other, is so frequently necessary, so here a similar 

 condition is found for nuclear reproduction." 



Auerbach supposes the two nuclei which appear at 

 opposite ends of the elongated egg to have arisen freely; 

 one of these comes from the end where the sperma- 

 tozoa had penetrated, the other from the opposite 

 end, where the germinal vesicle had disappeared. The 

 difference of origin influences the quality of the nuclear 

 materials arising, according to his conception, de novo; 

 fusion of the nuclei counteracts the differences thus aris- 

 ing; but all this would be undone if the division of the 

 fusion nucleus followed along the plane of the union; 

 hence the rotation through 90°. 



In the next year Biitschli again observed fusion of 

 nuclei in nematode eggs before the first cleavage. 

 However, he did not accept Auerbach's interpretation, 

 but he tended to regard it as a general law of nuclear 



