46 ANIMAL LIFE AND HUMAN PEOGRESS 



produces flowers, and the whole process is repeated from 

 generation to generation. 



Now the plant, with its special kind of roots, stem, leaves 

 and flowers, is a very diiierent-looking and much more com- 

 plicated thing than either the male or female germ. The 

 latter appear, even under the best power of the microscope, 

 almost structureless. Yet in them there must be some 

 principle capable of giving rise to the whole plant. That 

 principle must be (but exactly how we do not know) contained 

 in the substance or plasm of the germ-cell. And therefore 

 the " germ-plasm " must have an ultimate constitution of 

 extreme complexity. Also a constitution of a definite kind, 

 because the germ does not give rise to any kind of plant but 

 to a particular kind, having definite and recognisable characters 

 of stem, leaves, flowers and so forth. 



So we can see, dimly enough at first, that there must be 

 something in the germ-plasm which we may call a " factor " 

 {i.e. a thing which produces a result) for every individual 

 character that the plant exhibits. 



Exactly similar phenomena occur in animals. 



Now we know well that the individual plant or animal — 

 mankind himself — has an allotted term of life. The germ 

 grows into the individual, the individual comes to maturity ; 

 when mature it reproduces new germs, and sooner or later 

 after reproduction withers away and dies. The individual 

 dies but the new germs carry on the race. 



So the race does not die but is, potentially at least, im- 

 mortal. The individual, however, is mortal. This was recog- 

 nised clearly by Aristotle, and was a subject of deep reflection 

 to Harvey, who wrote : " Facit namque hie circuitus gallina- 

 cerjn genus sempiternum ; dum modo puUus, modo ovum, 

 continuata perpetuo serie ; ex individuis caducis et pereun- 

 tibus immortalem speciem producunt " (Bxercit. xxviii.). 

 (This is the round that makes the race of the fowl eternal ; 

 now pullet, now egg, the series is continued in perpetuity ; 

 from frail and perishing individuals an immortal species is 

 engendered.) 



It was Sir Francis Galton, by his theory of " Stirps," and 



