CHARLES DAEWIir. 131 



The simplest form of life of -which we can conceive, is a particle 

 of sarcode or protoplasm endowed with the power of movement, 

 so that it may change its form if not its place ; of assimilation, so 

 that it may increase in hulk ; and of fission, so that when it has 

 attained a certain size it may form two particles, this process of 

 division continuing, and thus causing the particles to increase in 

 number in geometrical progression. In each particle, however 

 minute, there must be two opposing forces, stability and mobility, 

 while growth, by assimilation of extraneous matter, implies change, 

 so that no living thing is precisely the same at any one period of 

 its life as it is at any other. 



Stability implies heredity, while mobility implies variabiKty. 

 Everything that lives must move and grow and multiply itself, 

 and therefore change its form and dimensions and numbers, and 

 if the food it assimilates be not always precisely the same, it 

 must also change its composition or constitution. Given, there- 

 fore, a single particle of protoplasm, the two particles into 

 which it divides will probably differ from one another, by 

 however so little, when they divide. 



Further, the molecules in every particle of protoplasm, vegetal 

 or animal, are as incessantly moving as are the molecules in 

 every particle of inert matter which is not absolutely cold, that 

 is, not at an absolute zero temperature. In this incessant 

 qiuvering or vibrating molecular motion, arises life in the one 

 case and warmth in the other, and therefore in the very 

 conception of the nature of life we cannot get rid of the idea 

 of alteration by internal as well as external movement. Thus 

 viewed, heredity is similarity resulting from stability, and 

 variability is dissimilarity resulting from mobility. 



Variability is thus as intelligible as is heretlity, and it is 

 certain that variations do occur and are perpetuated. In our 

 domestic animals and cultivated plants, the individuals of any 

 variety differ more from each other than do the individuals of 

 any species or variety in a feral state, and therefore it would 

 seem that domestication and cultivation induce variability. But 

 Nature gives the variations, Man merely accumulates those 

 which are useful to himself, by propagating only from his best 

 plants, and only allowing his best animals to breed, or at least 

 not allowing his worst to do so. With regard to the extent 

 of variation, it may suffice to state that the domestic varieties 

 of the same species differ more from each other in almost any 

 character which man has selected and tried to perpetuate, than 

 do the distinct species of the same genera in a feral state. 



