108 Life and Death, Heredity and Evolution 



6Q 



Figure 29. Chromosomes and their mating. A. Nucleus containing 

 the chromosomes, from the salamander. B. The 23 chromosomes in a 

 single cell of a male grasshopper, as seen under the microscope. C. 

 The chromosomes of B drawn separately and arranged so as to 

 show that the group consists of a series of 12, the two members of 

 each pair being of the same size and form. One chromosome (fifth 

 from the left in the upper row) is without a mate in the male; in the 

 cell of a female it has a mate. D. The members of the pairs after 

 mating. Each of the 12 structures (save one) is formed by the union 

 of the two members of a pair. E and F. Details of the mating of the 

 chromosomes in the cells of another species of grasshopper. In E only 

 two chromosome pairs are seen; in the pair to the right mating side 

 by side has begun, but is not complete. In F several pairs are shown, 

 fully mated. Each of the granules of .which the chromosome is com- 

 posed mates with a granule of corresponding size and position in the 

 other chromosome. B to D, after Robertson, 1908. E and F, after 

 Wenrich, 1916. 



