2 24 POPULAR SCIENCE MONTHLY. 



To compare heredity with memory explains nothing, of course, 

 since we know as little of the physical basis of the one as of the 

 other, but if the analogy be admitted it will prevent the too confident 

 insistence upon the theory that heredity depends entirely upon posi- 

 tional or other mechanical relations of molecules, or is in some way 

 embodied in particular granules or chromosomes. 



But even the most fantastic theories often have some basis of sug- 

 gestion in fact, and although we can not accept Professor Wilson's 

 cytological explanation of Mendel's laws, nor even share his hope that 

 cytology will elucidate evolution, it is by no means impossible that the 

 normal individual diversity of organisms has a cytological as well as 

 an evolutionary significance. That normal development or growth by 

 cell division is advantaged by cross-fertilization may mean that the 

 cells divide more readily and normally when they contain protoplasmic 

 'elements' of a proper degree of diversity than when they have only 

 one kind of protoplasm, as would happen in narrow inbreeding, and 

 also when cross-breeding is too wide for the intimate cooperation re- 

 quired for true fertilization. The Mendelian effect would then be 

 explainable on the suggestion of a partial cooperation which has to be 

 abandoned in the formation of new individuals, because, while the 

 organism can follow either of two diverging parental roads with re- 

 spect to any character, it is, as it were, a stranger to the path that an 

 average would require. 



The conjugation of cells may be viewed as a process quite distinct 

 from reproduction, though it is a necessary preliminary to the long 

 series of cell divisions required to build up the complex bodies of the 

 higher animals and plants. As we descend in the organic scale the 

 conjugating cells become more and more similar to each other and to 

 the so-called vegetative or somatic cells of which the body of the organ- 

 ism is composed. Among simple organisms all the cells are alilce, 

 including those formed immediately before and after conjugation, and 

 it is not strange that with the diversification of the cells which consti- 

 tute the various tissues of the plant or animal body the germ cells 

 should become specialized and unlike any of the others. The exist- 

 ence of special reproductive cells among the higher animals and plants 

 is therefore to be looked upon as corresponding to the general com- 

 plexity of the organism, rather than as an indication of a special 

 mechanism of heredity resident in the germ cells. As founders of new 

 cell-colonies or compound individuals they develop, it appears, on one 

 or the other of divergent parental lines instead of striking out on an 

 untraveled road between. 



JSTotwithstanding their great significance Mendel's laws are nega- 

 tive rather than positive in their bearing upon descent, since we do 



