Cmacallum] cellular OSMOSIS AND HEREDITY 16y 



and this explains their readiness to undergo alterations from the con- 

 dition of virulence to that of attenuation, or vice versa, in cultures, and 

 in the animal body. Only in a parasitic or saprophytic life could such 

 organisms continue their existence. The cells in the bilue-green algae are 

 protected by two membranes exteriorly, and they thus escape the résulte 

 of the direct action of the salts of their enviromnent, but their perpetua- 

 tion, probably almost unaltered, from a very remote period in the history 

 ci the gljobe, while other organisms liave not been so continued except 

 in species whicJi are the results of an ever progressive evolution, shows 

 what a handicap in evolutional modification these two external mem- 

 branes constitute. 



After the development of the nucleus came the differentiation into 

 sex, and this was an additional factor in promoting the function of 

 heredity, for the union of two germ plasmas, as occurs in the fertilization 

 of ova, simply doubles the certainty that the main ancestral characters 

 shall be transmitted to the offspring, and at the same time tends to com- 

 municate to aill the individuals of a species characters which may be of 

 immense advantage tO|it in evolution in the long run. 



From all that precedes, it may be gathered how important it is to 

 have a clear view of what osmosis fundamentally means from the phy- 

 siological side, and it may be understood that through a form of it the 

 cell nucleus which knows not the inorganic world, and which knows 

 neither fat nor free carbohydrates is the sacred receptacle for the hered- 

 ity-bearing substance, the germ plasma, alone. Through this concep- 

 tion of osmosis and of the function of the structure concerned, the 

 nuclear membrane, it may be seen what an all-important part a simply 

 physical property of matter, rightly comprehended, plays and has played 

 in the progressive evolution of living forms on our planet. 



