202 INDIVIDUALITY OF CHROMOSOMES [CH. 



bility of the chromosomes being connected with the trans- 

 mission of hereditary characters will be considered. On the 

 supposition that the chromosomes play an important part 

 in the life of the cell, and therefore of the development of an 

 embryo, BOVERI has based an ingenious argument in favour 

 of the belief that different chromosomes have different 

 functions in this respect. When in Echinoderms two sper- 

 matozoa enter an egg, as may happen if the egg is treated 



FIG. 26. Diagram of the distribution of chromosomes on a quadripolar 

 spindle, from BOVERI (1903 a}. 



with an anaesthetic before fertilisation, a quadripolar 

 spindle may result in the first segmentation division. Each 

 spermatozoon gives rise to two centrosomes, and these four 

 centrosomes become connected by four spindles, with the 

 result that the egg divides simultaneously into four blasto- 

 meres. Since there are, at the beginning, three nuclei (egg 

 nucleus and two sperm nuclei) each with the reduced num- 

 ber (n) of chromosomes, there are in all $n chromosomes 

 distributed in the equatorial plates of four spindles. And 

 since each chromosome divides and its halves pass to the 

 poles of its spindle, there will be altogether 6n chromosomes 

 distributed among the four daughter nuclei, or an average 



