112 



THE CHROMOSOMES 



rise to abnormal embryos, as several observers have 

 recorded. The result can best be attributed to the 

 irregular distribution of qualitatively different chro- 

 mosomes; only those embryos in which each cell has a 

 full complement developing normally. 



Boveri's evidence went still further, for he sepa- 

 rated the first cleavage cells of these dispermic eggs 



FIG. 37. Dispermic fertilization of egg of sea urchin. The four 

 centrosomes cause an unequal distribution of the fifty-four chromosomes, 

 leading at the first division to four cells which contain different num- 

 bers of chromosomes. 



and followed their history. Some of them gave rise 

 to perfect dwarf larvae. The number of normal 

 embryos was small, but was that expected on the 

 chance distribution of the chromosomes, for we 

 should expect to find in a few cases an isolated cell 

 that contained a full complement of chromosomes 

 and from such a cell a normal embryo would be 

 formed. The abnormality in development of the 

 rest of the isolated cells was not due to any harmful 



