CHE CARRIERS OF THE HERITAGE 17 

 p 



,. mighout all the various cells that make up the 



T. duals of any one species these chromosomes 



j ir to be practically constant in number with some 



', >tions to be mentioned later in connection with 

 wri 

 rpi This law of the constant chromosome number 



any species was first stated by Boveri in 190Q. 



he chromosomes of different organisms vary in 



iber from two in the worm Ascaris up to perhaps 



.0, according to Haecker ('09), in certain radiolaria. 



3cies which apparently are closely related may 



fer widely ^with respect to the number of their 



romosomes, while species of unquestionably re- 



ote relationship may have an identical number of 



iromosomes in each of their cells. The number of 



iromosomes characteristic for a species, therefore, 



j in no way an index to the complexity or degree of 



iifferentiatiori of the species. 



Besides the nucleus there may often be identified 

 t n the cytoplasm of the animal cell a tiny body known 

 as the centrosome. At certain times in the life-cycle 

 of a cell the centrosome becomes the focal point of 

 peculiar radiating lines, which play an important 

 part in the behavior of the cell, particularly during 

 the period of division. ^ 



Every cell passes through a cycle of life which may 

 be compared with that common to individuals. It 

 is born from another cell ; passes through a vigorous 

 youth characterized by growth and transformation ; 

 attains maturity when the metamorphoses of its 

 earlier life give place to a considerable degree of 

 stability ; and finally, after a more or less extended 



