HYBRIDIZATION IN ANIMAL BREEDING 519 
The male mule apparently never produces functional spermatozoa, 
Wodsedalek has found that the horse and ass have different numbers of 
chromosomes, so that the mule comes from the union of an egg-cell con- 
Fie. 200.—A mare mule (?) with a foal by a Percheron stallion. (After Lloyd-Jones.) 
Fic. 201.—The foal of Fig. 200. It is said to exhibit mule-like characters in its feet 
and actions, although otherwise its characters are all horse-like. (After Lloyd-Jones.) 
taining nineteen chromosomes with sperm cells containing either thirty- 
two or thirty-three. In consequence reduction divisions in the mule 
are prevailingly abnormal as to chromatin distribution, and no functional 
spermatozoa appear to be produced. If we judge by analogy with plants, 
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