CHAPTER III 



DIFFERENTIATION OF STRUCTURE AND DIVISION 

 OF LABOUR 



WE have seen that plants and animals may be 

 arranged in an ascending series, rising in the case 

 of plants from such a type as that figured on p. 19 

 to the large and vastly complicated forest tree, or 

 in the case of the animal world, from the simple 

 Amoeba (Fig. 3) up to such an elaborate mechanism 

 as man himself. 



The very lowest types of both series of forms, 

 simple as they are, are yet living organisms capable 

 of performing all the functions we have recognised in 

 Vaucheria and in the frog. Each consists of a minute 

 mass of protoplasm with a central granule or nucleus 

 and, in some cases, one or more chloroplasts. Micro- 

 scopic examination of a higher plant or animal 

 show's us that each is composed of units of extremely 

 varied size, shape and structure, yet every unit, at 

 least when young, consists of protoplasm and a 

 nucleus. Such a unit we term a cell, and we are thus 

 able to say that some plants and animals the lowest 

 in the scale are unicellular, while others the 

 majority are multicellular. 



Let us glance first at unicellular forms and for that 

 purpose we may select for study a simple animal, 

 Amoeba, often met with in fresh water aquaria, and 

 the plant commonly known as Pleurococcus, which, 

 together w r ith forms closely allied to it, gives the 

 familiar green colour to the bark of trees, rain butts, 



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