i MORPHOLOGY AND PHYSIOLOGY 9 



colourless heart. It is called the contractile vacuole^ and 

 consists of a cavity in the ectosarc containing a watery 

 fluid. 



Occasionally Amoebae or more strictly Amoeba-like 

 organisms are met with which have neither nucleus J nor 

 contractile vacuole, and are therefore placed in the separate 

 genus Protamceba (Fig. 2). They may be looked upon as 

 the simplest of living things. 



The preceding paragraphs may be summed up by saying 

 that Amoeba is a mass of protoplasm produced into tempo- 

 rary processes or pseudopods, divisible into ectosarc and 



' A B C D ^HP^F 



FrHv.^2 Protam&ba primitive*, ; A, B, the same specimen drawn at 

 short intervals of time, showing changes of form. 



C E. Three stages in the process of binary fission. (After Haeckel. ) 



endosarc, and containing a nucleus and a contractile vacuole : 

 that the nucleus consists of two substances, chromatin and 

 achromatin, enclosed in a distinct membrane : and that the 

 contractile vacuole is a mere cavity in the protoplasm con- 

 taining fluid. All these facts come under the head of 

 Morphology, the division of biology which treats of form 

 and structure : we must now study the Physiology of our 

 animalcule that is, consider the actions or functions it is 

 capable of performing. 



1 Judging from the analogy of the Infusoria it seems very probable 

 that such apparently non-nucleate forms as Protamoeba contain chroma- 

 tin diffused in the form of minute granules throughout their substance 

 (see end of Lesson X., p. 118), or that they are forms which have lost 

 their nuclei. 



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