INTRODUCTION ii 



alone concerned with the task of reproduction. They are 

 nourished by the body, and on attaining maturity, give 

 rise to new bodies. These reproductive cells are exces- 

 sively small. The male, or " sperm " cell, can only be 

 distinguished under the highest powers of the microscope. 

 The female cell, or " Ovum," is always larger than the 

 male, because, in addition to the germinal matter which 

 it contains, it is furnished with a store of food in the 

 shape of yolk. This accounts for the relatively enormous 

 size of the egg of the hen. Within the hardened shell 

 the germ develops into the chick, deriving food for its 

 growth from this generous store. Where this yolk is 

 limited in quantity the growing body is hastily fashioned, 

 and launched forth into the world in the form of a " larva," 

 when it must forage for itself till it has attained its adult 

 form. Or it is retained within the body of the mother 

 until development is complete. 



The reproductive cells are the bearers of the Germ- 

 plasm, the stuff of which man and the beasts of the field 

 alike are fashioned. Only a portion of this germ-plasm 

 gives rise to a new body ; the rest is, as it were, held 

 over and stored within the new body to give rise to 

 another in due course. That which produces the body we 

 call the " Somatoplasm," because it is the " plasm " or 

 stuff of which the " Soma," or body, is made. As to 

 the nature of this Germ-plasm and its mysterious 

 properties, a wide divergency of opinion exists among 

 savants. But the views which find most favour to-day 

 are those of the veteran Professor August Weissmann, as 

 set forth in his work on the " Germ-Plasm, a Theory 

 of Heredity." 



The excessively minute quantity of this germ-plasm 

 which suffices to form a new body is incredible. By what 



