18 



CELLS AND THEIR PARTS 



Owing to the plant-cell having a wall of cellulose, a sub- 

 stance chemically allied to starch, and owing to the fact that 

 many plant-cells develop hard, woody skeleton-cells formed 

 of lignin or a thick- 

 ened cuticle, the 

 higher plants are 

 usually much more 

 stiff and rigid than 

 the higher animals. 

 It is much harder to 

 plunge a dagger into 

 an oak than into a 

 man. Both animals 

 and plants contain 

 an enormous per- 

 centage of water, and 

 this is equally true of 

 the higher animals. "^ 

 Even the Archbishop 

 of Canterbury com- 

 prises 59 per cent, 

 of water. When you 

 once traverse the 

 skin, the interior of 

 the body of a Verte- 

 brate is about as soft 

 as a very weak jelly. 

 It is, indeed, semi- 

 fluid, and thus the 



enormous numbers of ^^^ ^ ^^jj ^^^^ ^ j^^^^ ^^^^^ magnified: at 

 parasites which make the exterior is the ceU-waU, which encloses the 

 their way into the body: the latter is composed of a protoplasmic 

 bodies of animals are ^^ ^^Y"^ surrounds the large watery vacuoles, 



while m the centre the nucleus is suspended by 

 able to push their way bridles of protoplasm. The arrows indicate the 

 through the various movements of the protoplasm during life. From 



tissues and arrive ^"^®^- 



at the site they seek. Many animals are encased in external 

 skeletons which protect their interior. Examples of these are 

 the shells of molluscs, the hard casings of insects and lobsters, 



