82 PROBLEMS OF FERTILIZATION 



one sperm nucleus, the other only the chromosomes of 

 the supernumerary sperm nucleus. In the case of tri- 

 spermy we have three karyokinetic figures one diploid, 

 two haploid. The dispermic egg divides in two cells 

 and the trispermic in three, but each of these cells 

 is binucleated. In the dispermic egg one nucleus of 

 each cell is diploid, the other haploid; in trispermic 

 eggs this applies to two of the cells, but the two 

 nuclei of the third cell are both haploid. In subse- 

 quent divisions the proportions of diploid nuclei is main- 

 tained. 



In the sea urchin, in the frog, and also in all other 

 cases so far as known, pathological polyspermic eggs 

 produce abnormal embryos, which soon die. Boveri 

 has made a most careful and interesting analysis of 

 conditions in the sea urchin, which led him to the 

 conclusion that the ill effects are due in this case to 

 abnormal distribution of the chromosomes. Taking 

 the simplest case of dispermy he shows that the distri- 

 bution of chromosomes in the tetraster is highly irreg- 

 ular and a matter of chance, from which it results 

 that the four nuclei formed have different numbers of 

 chromosomes. This would not in itself account for 

 the abnormal results, because it is known that half 

 the diploid chromosome number is sufficient for normal 

 development, and he could show that the number in 

 each nucleus exceeds this number on the average. 

 From this he argues that the chromosome composition 

 of the nuclei must be on the average inadequate; that 

 not merely a given number of chromosomes, but a defi- 

 nite qualitative composition of the chromosome group, 

 is necessary for normal development. He thus con- 



