THE CHROMOSOMES 145 
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 
7 
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 larve. 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 
