ZOOLOGICAL SCIENCE 203 



final analysis, cell problems is again illustrated by the 

 present affiliation of genetics with cytology. 



Cytology, or the science of the cell, concerns itself with 

 structure and function in cells of every sort. But the 

 cytologist has been so occupied with the germ-cells and with 

 the early phases of development that cytological investiga- 

 tion to date is almost a synonym for germ-cell investigation. 

 Germ-cells or gametes are the links between successive 

 generations. Every many-celled animal is at one period of 

 its life-cycle encompassed within the limits of the single cell 

 formed by the united ovum and spermatozoon. The gametes 

 have naturally assumed an overwhelming importance in 

 cytology. They are no less important in genetics, because 

 the latter science must know how adult characteristics are 

 transmitted through the germ-cells to the next generation. 

 Genetics and the cytology which deals with germ-cells are 

 but different aspects of the same fundamental problem. 



We have already described the probable mechanism of 

 Mendelian heredity as it appears in the chromosomes. The 

 interlocking of genetics and cytology was inevitable, once 

 the facts regarding the gametes had been established and 

 once Mendel's epoch-making discovery had become gener- 

 ally known. The chromosomes of the ripening germ-cells 

 were found to behave in a peculiar manner. Mendelian 

 unit-characters were found to be inherited in a fashion 

 equally distinctive. Suddenly it was realized that the 

 chromosomes offered an explanation of the segregation 

 which is the essential feature of Mendelian inheritance 

 (c/. Fig. 20). 16 Thus the experimental results of genetics 

 became of interest to cytology and the results of cytological 

 study assumed importance for genetics. The latter science 

 has arisen upon an experimental foundation in the breeding 



18 Wilson, E. B., "Mendel's Principles of Heredity and the Maturation of 

 the Germ-Cells," Science, Dec. 19, 1902. This brief paper summarizes the 

 evidence at a time when the cytological mechanism, which has since become 

 familiar, was just beginning to be understood. 



