204 INDIVIDUALITY OF CHROMOSOMES [CH. 



BOVERI points out. Some larvae from dispermic eggs are 

 completely normal; others develop normally up to the gas- 

 trula stage, or even later, but lack the skeleton in one half 

 or one quarter of the larva in the pluteus stage ; while others 

 begin to show abnormalities in the blastula and fail to be- 

 come gastrulae. Furthermore, if the blastomeres of a normal 

 four-cell embryo are shaken apart, each produces a complete 

 small larva, but the separated blastomeres of a dispermic 

 egg are rarely able to do this, although some proceed very 

 much further in development than others. Now the only 

 difference between the four cells of a dispermic egg is in the 

 chromosomes ; if abnormalities are induced in the cytoplasm 

 they must be common to all four cells. Since, therefore, 

 these cells differ widely from one another in their powers 

 of development, it must be because some have received 

 chromosomes that are absent from others. 



This kind of argument cannot be regarded as a conclusive 

 proof of the functional individuality of chromosomes; it 

 rather assumes that individuality, and shows that the results 

 observed are easily explicable on that assumption, but are 

 hard to account for otherwise. A weak point in the argu- 

 ment is that in polyspermic eggs of the frog, as described 

 by BRACKET (1917), the early development maybe normal, 

 and yet the larvae die after hatching, although the conditions 

 are such as to exclude BOVERI'S interpretation. In poly- 

 spermic frog's eggs one spermatozoon conjugates with the 

 egg-nucleus, while the others form independent nuclei in 

 -connection with each of which a spindle develops, and the 

 egg divides into as many blastomeres as there were sperma- 

 tozoa. In the resulting embryo, therefore, some nuclei con- 

 tain the diploid, others the haploid number of chromosomes, 

 but every cell contains at least the whole haploid series, 

 and yet, when the embryo becomes a larva, it is not able to 



