THE CELLULAR BASIS OF HEREDITY 235 



denominations. If these cards are then dealt into two hands, one card 

 of each pair going to one hand and the other to the other hand, we will 

 have two cards of each denomination in each hand, but if the cards are 

 dealt indiscriminately some of them will be red and some black. This 

 description parallels what takes place in the maturation of the human 

 ovum, except that there is no evidence that there are more than two 

 suits of chromosomes, one maternal and the other paternal. 



To carry out this comparison in the case of the maturation of the 

 human sperm where there are only 47 chromosomes it is necessary to 

 take another pack and discard an additional card, say the queen of 

 clubs; then in the union of corresponding red and black cards into 

 pairs the queen of hearts unites with the queen of spades, but the queen 

 of diamonds remains alone, and when the cards are dealt into two hands 

 as before one hand will contain 24 cards and the other 23. 



If now we complete this comparison by extending it to what takes 

 place in fertilization we must take one hand from each of these deals 

 and put them together into one pack; though this pack would contain 

 cards of every denomination there would be varying numbers of red and 

 black cards and a mixture of cards from two distinct packs. In no 

 game of cards do corresponding cards from different packs have slightly 

 different values nor are half of the cards taken from one pack and half 

 from another (at every game), but this is just what happens in the 

 shuffle and deal of the chromosomes. Because of the mixture of chro- 

 mosomes from distinct individuals in every generation, each of which 

 has its own peculiar value, the game of heredity becomes vastly more 

 complex than any game of cards. 



This illustration may serve to make plain the fact that the pur- 

 pose of maturation and fertilization is, in part, this shuffle and deal of 

 the chromosomes, and its result is that every oosperm and every in- 

 dividual which develops from it is different from every other one. 



This conception of the specificity of every germ cell, as well as of 

 every developed individual, sets the whole problem of heredity and 

 development in a clear light. The visible peculiarities of an adult 

 become invisible as development is traced back to the germ, but they do 

 not wholly cease to exist. Similarly, the multidinous complexities of 

 an adult fade out of view as development is traced to its earliest stages, 

 but it is probable that they are not wholly lost. In short, the specificity 

 of the germ applies not merely to those things in which it differs from 

 other germs, but also to characters in which it resembles others — in 

 short, to hereditary resemblances no less than to hereditary differences. 



The mistake of preformation was in supposing that germinal parts 

 were of the same kind as adult parts ; the mistake of epigenesis was in 

 maintaining the lack of specific parts in the germ. The development 

 of every animal and plant consists in the transformation of the specific 

 characters of the germ into those of the adult, but not in the formation 



