170 



GENERAL BIOLOGY 



paired. Below this, the anaphase of the first, and the telophase of the 

 second polar division, leaves three chromosomes in the egg. 



The fifth grouping on the right is the metaphase group of the first 

 spermatocyte division with paired regular chromosomes and a single 

 X-chromosome. Below this, the diagrams of the first (unequal) and the 



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a 



I Ml 



Fig. 83. 



Diagram of chromosome-cycle of Phyllaphis coweni. See text for explanation. 

 ( After Doncaster. ) 



second (equal) spermatocyte divisions, leading to the ultimate sperm- 

 cell with three chromosomes and a small degenerate cell with two. 

 When the egg and sperm again unite in fertilization, the original six 

 chromosomes are restored and the egg is again as we see it at the top. 



From what has been said, it can be plainly seen that in all organ- 

 isms where there is an X-chromosome, this extra particle (as it does not 



