ORGANIC CHEMISTRY AND CELJ, DIVISION: : 19 1 



From what we shall soon learn regarding Paramoecia we know that 

 the chromosomes are the important carriers of all physical traits inher- 

 ited by a child from the parent. But, unless there is some method by 

 which the chromosomes throw off one-half their number, each child, 

 being the result of an egg and a sperm mating, would possess every- 

 thing its mother possessed, plus everything its father had. A super-race 

 would thus be produced which in a very few generations would be to- 

 tally unlike any of its parents. One can imagine what it would mean 

 to have every child twice as strong, and twice as tall, as its parents. 

 It would not be long before men would be thousands of feet tall, and 

 there would be little room for more than one of two people in the world. 

 But Nature apparently loves an average, and so somewhere, the chro- 

 mosomes are halved. 



The ripening process is known as the maturation division (Fig. 30). 

 The egg varies from the sperm in the number of complete function- 

 ing cells it produces, although the chromatin acts alike in both cases. 



From the primordial egg cell only one mature egg develops, while 

 three undeveloped eggs, called polar bodies, are formed. These latter 



degenerate and have no known func- 

 tion. Each sperm cell, however, de- 

 velops into four complete functional 

 spermatozoa, any one of which may 

 fertilize an egg. 



Notwithstanding this difference, 

 both sperm and egg cell have the same 

 number of chromosomes characteristic 

 of the species. This full quota of 

 chromosomes is called the diploid num- 

 ber. 



The primordial cells (those which 

 are to become eggs) begin their growth 

 very early in the embryo. Usually, 

 there is a quantity of yolk deposited to 

 serve as food for the embryo which is 

 in turn to develop from the egg. 



The chromatin in the nucleus 



sperm\ 



\ / 



I I I I 



Fig. 31. 



A. Diagram of the derivation of the sex gathers in a thick mass towards one 



side of the nucleus. This is known as 

 the synapsis stage. From this thick 

 mass of chromatin there will emerge 



crease in number and diminution in size j us t one-half the number of 



cells. 2., the fertilized egg (zygote) 

 som., the body plasm (soma) ; t., the de- 

 velopment period during which the germ 

 plasm and the body plasm are indistinguish- 



(the number of divisions is much greater 



than shown) : r., the period of increase in SOmCS USUally found in Cells of the 



dze with differentiation of cytoplasm ; w., 



the two maturation divisions; pb., polar ticular SpCClCS WC are Studying. Such 



cells are said to have the haploid num- 



bodies ; e., egg. (After Boveri.) 



B. Spermatozoa of Rana esculenta. 



C. Spermatozoa of Rana fusca. 

 Leydig.) mp., middle piece. 



(After 



chromosomes. 



