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CHAPTER VI. 



UNICELLULAR ANIMALS PROTOZOA. 



AAfCEBA. 



IN order to emphasise the distinction between a unicellular 

 animal and a unicellular plant, we devote this chapter to a 

 sketch of the organisation and life-history of one of the 

 simplest of the animal forms, viz. Amoeba. 



Much of what has been said of protoplasm in general 

 is applicable here. Indeed, as will be seen on reference to 

 Chapter II., Amoeba was there instanced as an example of 

 protoplasm in one of its simplest and most easily accessible 

 forms. It may be well, however, to repeat briefly the main 

 points there discussed in detail. 1 



Amoeba (fig. 18), as there stated, has generally the ap- 

 pearance of a minute particle of transparent or finely granular 

 jelly, having a nucleus, contractile vacuole, and granules, 

 and showing an elementary differentiation into ecto- and 

 endo-sarc. During its life it is constantly undergoing slow 

 changes in form, due to the protrusion and withdrawal of 

 masses of its own substance (pseudopodia). Its method of 

 ingesting and circulating food-material has already been de- 

 scribed (p. 34). Careful observation shows that the con- 

 tractile vacuole undergoes periodic changes of form which 

 partake of the nature of alternate swellings and contractions, 

 known technically as diastole and systole. It is probable 

 that the contractile vacuole is some sort of renal organ 



1 It is advisable that the student re read Chapter II. in this relation. 



