44 



AGE, GROWTH, AND DEATH 



in this picture are beginning to appear. It is fibrils 

 of this sort which we find as the main elements in 

 the constitution of sinews and tendons, as, for in- 

 stance, the tendon of Achilles, at the heel. In a very 

 young body we find there are but few fibrils ; in the 

 adult body an immense number. 



If we are to be scientifically exact we must note 



FIG. 8. EXAMPLE OF A SYNCYTIUM. Embryonic connective tissue from the 

 umbilical cord of a human embryo of about three months, magnified about 

 400 diameters ; t, c, cells ; f, intercellular fibrils. 



that in the early stages of vertebrates, the germ or 

 embryo is not constituted of discrete cells. There 

 are nuclei, and each nucleus is surrounded by proto- 

 plasm. Each nucleus is perfectly individualised, but 

 its protoplasm merges into that about the neigh 



