260 RECENT CYTOLOGY 
the separate members of each of the two half-tetrads 
pass to opposite poles (Figs. 35, 36). In the nucleus 
of each of the four cells which thus arise there is, there- 
fore, present one quarter of each of the four chromo- 
somes which originally appeared—one member, that 
is to say, of each tetrad (Fig. 37). Each of the cells of 
which we have thus traced the origin develops directly 
into a single spermatozoon. 
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The method of development, or maturation, of the 
ova, or egg-cells, of animals is in all essential respects 
similar to the process by which the spermatozoa arise. 
It differs, however, in the fact that of the four cells 
which result from the corresponding divisions, one is 
very large and constitutes the ovum, whilst the other 
three are very minute, and are apparently of no further 
importance. In the accompanying diagrams (Figs. ‘40 
to 42), the smaller cells, or polar bodies, have been 
