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THE BRIDGE OF LIFE 



Photos by Winchester 



Fig. 31.5. Spermatogenesis as seen in living grasshopper cells from the testes. A 

 primary spermatocyte (A) is preparing to undergo meiosis. In the early prophase of 

 the first division of meiosis (B) the slender chromosomes can be seen after they have 

 paired. The diploid number of this grasshopper is 23; thus there are eleven pairs 

 and one unpaired (X -chromosome). In a latter prophase (C) it can be seen that each 

 chromosome is double; thus there are four chromatids to each pair. Crossing over 

 between chromatids of the paired chromosomes is evident. The X-chromosome at the 

 upper part of the cell is unpaired and, therefore, shows no crossing over. In the 

 metaphase (D) the chromosomes are greatly shortened as they line up in the center 

 of the spindle. In the anaphase (E) the chromosomes have pulled apart. The 

 chromatids have separated from one another everywhere except at the centromere end. 

 This gives a V-shape to the chromosomes. Note the eleven chromosomes in the lower 



