I MORPHOLOGY AND PHYSIOLOGY 9 



Occasionally Amcebse — or more strictly Amoeba-like 

 organisms — are met with which show neither nucleus ^ nor 

 contractile vacuole, and are therefore placed in the separate 

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

 the simplest of living things. 



^r 



iJ5 



B ^^^E 



Fig, 2 — Protanitxba primitiva , 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 



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

 that such apparently non-nucleate forms as Protamceba 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. 



