56 
SPERMATOGENESIS OP NORMAL 
a tendency which exists in the primary spermatocytes of normal 
appearance, which are to be found in all hybrids. 
9. The above conception may likewise afford a clew to 
the problem of why certain plants will come true from slips or 
grafts, but not from seed. The explanation may be sought in 
the pseudo-reduction period of the germ-cell. 
10. The deformed spermatozoa are due to the incomplete 
development of the nucleus of the spermatid to form the head. 
11. It is suggested that the physical basis of heredity may 
be dual in nature, involving both cytoplasm and chromatin. 
Hull Zoological Laboratory, 
The University of Chicago^ May lo, igoo. 
