10 MICROSCOPIC .ANATOMY OF THE TEETH 



throughout the organic world, and as Professor Huxley says : 

 ' The primordial germs of a man, a dog, a bird, a fish, 

 a beetle, a snail, and a polype, are in no essential structural 

 respects distinguishable. In this broad sense it may with 

 truth be said that all living animals, and all those dead 

 faunae which geology reveals, are bound together by an all- 

 pervading unity of organization." 



Especially since Darwin's time, the study of the cell and 

 its relations to heredity has greatly occupied the attention 

 of naturalists, and ' microscopic anatomy has shown us the 

 nature of the material on which organic evolution has 

 operated '. 



We have to distinguish between the ' somatic ' or body 

 cells and the ' germ ' cells. 



The somatic cells build up the body of the individual, the 

 germ cells are the racial cells, and the phenomena of heredity 

 depend on their continuance from one generation to another. 

 The germ cell, according to Weismann, is immortal ; the 

 somatic cell perishes with the individual body. 



As Wilson says (9) : ' The cell theory must be placed beside 

 the evolution theory as one of the foundation stones of 

 modern biology these two great generalizations have been 

 developed along widely different lines of research, and have 

 only within a very recent period met upon a common 

 ground.' The cell nucleus is shown to be the vehicle of 

 inheritance, and, as this author further states, * thus the 

 wonderful truth became manifest that a single cell may 

 contain within its microscopic compass the sum total of 

 the heritage of the species. The death of the individual 

 involves no breach of continuity in the series of cell divisions 

 by which the life of the race flows onwards the individual 

 body dies, it is true, but the germ cells live on, carrying 

 with them, as it were, the traditions of the race from which 

 they have sprung, and handing them on to their descendants ; 

 the body is merely the carrier of the germ cells which are 

 held in trust for coming generations.' 



Another question which has led to much controversy is 

 whether characters acquired during the lifetime of the 

 individual are capable of being transmitted to the offspring. 

 This much-debated theory was formulated by Lamarck in 



