Heredity and the Origin of Variations. 131 



tion. If, now, we express the development of tissues and 

 the sequence of organisms in the following scheme, the 

 continuity of the reproductive cells will be apparent : 



^Skeletal and protective cells 



Reproductive cell C^^ SM^ cells 

 > cells 



Reproductive 



It is clear that there is a continuity of reproductive 

 cells, which does not obtain with regard to nerve, gland, or 

 skeleton. If, then, we class together as body-cells those 

 tissue-elements which constitute what we ordinarily call 

 the body, i.e. the head, trunk, limbs all, in fact, except the 

 reproductive cells, our scheme becomes 



Reproductive ceUO^ductive cells O^froductive cells O 



From this, again, it is clear that the body does not pro- 

 duce the egg, or reproductive cell, but that the reproductive 

 cell does produce the body. Of course, it should be noted 

 that we are here using the term " body " as distinguished 

 from, and not as including, the reproductive cells. But this 

 is convenient, in that it emphasizes the fact that the mus- 

 cular, nervous, skeletal, and glandular cells take (on this 

 view) no part whatever in producing those reproductive 

 cells which are concerned in the continuance of the species. 



Such, in brief, is the view that the egg produces the 

 hen. We will return to it presently when we have glanced 

 at the alternative view that the hen produces the egg. 



On this view, the reproductive elements are. not merely 

 cells, the result of normal cell-division, which have been 

 set aside for the continuance of the species. They are, so 

 to speak, the concentrated extract of the body, and con- 

 tain minute or infinitesimal elements derived from all the 

 different tissues of the organism which produces them. 

 Darwin * suggested that all the cells of the various tissues 

 produce minute particles called gemmules, which circulate 



* Darwin, " Animals and Plants under Domestication," 2nd edit., vol. ii. 

 chap, xxvii., from which the following description and quotations are taken. 



