The Cellular Basis 173 



sexual reproduction. In asexual reproduction the in'dividual var- 

 iations which occur are chiefly if not entirely due to environment, 

 but in sexual reproduction they are also due to new combina- 

 tions of hereditary elements. The particular germinal organiza- 

 tion transmitted from one generation to the next depends upon 

 (a) the ancestral organization, (b) the particular character of 

 the cell divisions by which the germ cells are formed, (c) the 

 particular kinds of egg and sperm cells which combine in fertil- 

 ization. The ancestral organization determines all the general 

 characteristics of race, species, genus, order, phylum. It deter- 

 mines the possibilities and limitations of individual variations. 

 Given a certain ancestral organization, the individual peculiarities 

 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, 

 viz., 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 

 in the human oocyte; 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 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 



