308 



SCIENCE PROGRESS 



basis of inheritance ; it has shown that plants and animals are 

 reproduced on the same common plan of a dual inheritance 

 from the male and female germs. Let us briefly consider the 

 union of the male and female germs of fertilisation in the 

 higher animals, for it will help you to understand some of the 

 problems of inheritance. 



The male germs are formed in countless millions in the male 

 reproductive organs. The female germ-cells, ova or egg-shells, 

 are contained in the ovaries ; they are about 40,000 in number 

 at birth, and the germ which constitutes the material basis of 



p&.i 



Fig. 4. 



1) Diagram of egg-cell before ripening. (2) Maturation or ripening of the ovum casting out of half of the 

 nucleus to form the first polar body. (3) Formation of second polar body and entry of spermatozoon (S) 

 into egg. (4) Approximation of (M) male and (F) female germs. (5) Enlarged diagram of the two 

 germs (F and M) before the first cleavage of the egg. (6) Enlarged diagram of egg after first cleavage. 

 P. Bi, first polar body ; P. B2, second polar body; S. sperm; Ni and N2, nuclei of first two cells 

 of the organism containing representative particles (germinal determinants) of (F) the female germ and 

 (M) the male germ. 



inheritance is a minute round body in the cell (fig. 4, F). When 

 the ovum ripens (2, 3), which occurs periodically, one half of 

 this germ is cast out of the cell. Why is this ? It is to make 

 way for a union with the incoming male germ, the bearer of the 

 potential inheritance from the male, as the female germ is from 

 the female. These two germs constitute the woof and the warp 

 of the material basis of inheritance ; while the male germ brings 

 in a body called the centrosome, which acts as the shuttle which 

 weaves the woof into the warp. The main substance of the 



