APPLICATION TO METAZOA. 133 



curious, the utterly sterile male hybrids from the 

 pheasant and the fowl act in the same manner, 

 'their delight being to watch when the hens leave 

 their nests, and to take on themselves the office of 

 a sitter.' "i 



When we consider these facts and remember how 

 large a part of all the instincts and activities of ani- 

 mals are dependent upon the influence of the germ- 

 cells, it seems highly probable that the growth and 

 activity of an animal should exert a retroactive in- 

 fluence on the germ-cells. 



In most animals the period for the ripening or 

 maturation of the germ-cells is determined by the 

 changes of season — influences which can only affect 

 the germ-cells through the medium of the body. 

 Finally, since the germ-cells possess the potentiality 

 of producing all the nervous and mental traits of the 

 body from which they are derived, we cannot sup- 

 pose them utterly disconnected from the nervous 

 system and inaccessible to its influence. There 

 seems to be a most profound and intimate connec- 

 tion between the two. 



We find, therefore, no essential difference between 

 the development and reproduction of the protozoa 

 and the same process among the metazoa. If in- 

 heritance of acquired characters be admitted for 

 I Vol. II., pp. 26, 27. 



