SEGREGATION OF GERM-CELLS 347 



camps, one half containing the dominant character in potentia (d), 

 and the other half containing the recessive character (r). This 

 occurs in both males and females, so that when inbreeding 

 takes place the possibilities are expressible thus : 



D(R) produces (50 with (d) 50 with (d)l D(R) produces 100 



100 egg-cells \50 with (r) 50 with (r)/ sperm-cells 



( 1 ) 25 egg-cells (d ) fertilised by 2 5 sperm-cells (d ) = 2 5 fertilised gametes (d ). 



(2) 25 „ (d) „ „ „ (r) = 25 „ „ (dr). 



(3) 25 „ (r) „ „ ., (d) = 25 „ „ (dr). 



(4) 25 „ (r) (r) = 25 ., „ (r). 



To sum up, 25 (d) developing into 25 pure D. 

 50 (dr) „ „ 50 D(R). 



25 (r) ,, ,, 25 pure R. 



Mendel's Theory summarised. — Mendel discovered an im- 

 portant set of facts, and he also suggested a theoretical inter- 

 pretation — the theory of gametic segregation. As Mr. Bateson 

 says, " The essential part of the discovery is the evidence that 

 the germ-cells or gametes produced by cross-bred organisms 

 may in respect of given characters be of the pure parental types, 

 and consequently incapable of transmitting the opposite char- 

 acter ; that when such pure similar gametes of opposite sexes 

 are united in fertilisation, the individuals so formed and their 

 posterity are free from all taint of the cross ; that there may 

 be, in short, perfect or almost perfect discontinuity between 

 these germs in respect of one of each pair of opposite characters." 



How the Segregation of Gametes might be effected. — Mendel 

 assumed that the hybrid offspring (of two pure-bred parents 

 differing markedly as to a unit character) produce two kinds 

 of germ-cells, one kind with the dominant character, the other 

 kind with the recessive character. This is the theory of the 

 segregation of gametes into two sets of "pure" gametes, and, 

 as we have seen, it harmonises well with the facts. 



But it may be asked if there is any known process by which 

 such a segregation could be brought about during the history 

 of the germ-cells. Is it enough simply to say that the germ- 

 cells are little living unities with an organisation, an equilibrium, 

 of their own, and that they tend, as they multiply, to become 



