I MORPHOLOGY AND PHYSIOLOGY 9 



Occasionally Amoeba; or more strictly Amoeba-like 

 organisms are met with which show neither nucleus 1 nor 

 contractile vacuole, and are therefore placed in the separate 

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

 the simplest of living things. 



%A m 

 ^ B C D 





FIG. 2 Protamxba primiliva , 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.) 



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 

 endosarc, and containing a nucleus and a contractile vacuole : 

 that the nucleus consists of two substances, chromatin and 

 nuclear sap, 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. 



First of all, as we have already seen, it moves, the move- 

 ment consisting in the slow protrusion and withdrawal of 

 pseudopods. This may be expressed generally by saying 



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. 120), or that they are forms which have lost 

 their nuclei. 



