176 Heredity and Environment 



of the germ cells are determined by the particular character of 

 cell division by which the germ cells are formed, and the peculiari- 

 ties of the individuals or persons which develop from these cells 

 are determined in large part by the particular kinds of germ cells 

 which unite in fertilization. 



Comparison of Cards and Chromosomes. The behavior of 

 chromosomes in maturation and fertilization is like the shuffle 

 and deal of cards in a game, and apparently with the same object, 

 namely, never to deal the same hand twice. To make this compari- 

 son more complete suppose that kings be discarded from the 

 pack, leaving 48 cards of two colors, red and black, which we will 

 compare to the 48 chromosomes of maternal and paternal origin ; 

 suppose that in the shuffling of these cards corresponding cards of 

 the red and black suits are temporarily stuck together so that the 

 ace of diamonds is united with the ace of clubs, the queen of 

 hearts with the queen of spades, etc., thus forming 24 red-black 

 pairs of the same 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 denomina- 

 tion in each hand, but if the cards are dealt indiscriminately each 

 hand may contain two black cards of any denomination, two red 

 cards or one black and one red- This description parallels what 

 takes place in the maturation of the human germ cells, except that 

 there is no evidence that there are more than two suits of chromo- 

 somes, one of which is maternal and the other paternal. 



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 ; this pack would 

 contain cards of every denomination from ace to queen but there 

 would be varying numbers of red and black cards and a mixture 

 of cards from two distinct packs. In no game of cards 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 chromosomes from dis- 



