POLYPLOIDY AND POLYSOMY 



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Fig. 19. — Meiosis in the egg of the horse thread worm Ascaris megalocephala, a race 

 with two diploid chromosomes. Left: the normal series ending in fusion of single 

 egg and sperm chromosomes. Right: the result of a misorientated first division 

 spindle is the failure of expulsion of the first polar body which fuses with its sister 

 nucleus. The second division leaves a diploid egg which is fertilized to give a 

 triploid embryo. Fusion with a similarly exceptional diploid sperm would give a 

 tetraploid of the race which is indeed found in nature (after Boveri, 1904). 



EUmenli of (j::i!<:ik!i 



97 



