55 



CHAPTER IV. 



THE MORPHOLOGY AND PHYSIOLOGY OF THE SIMPLEST 

 LIVING ORGANISMS PROTISTA. 



SECTION I. PROTISTA PROTAMCEBA. 



IN the preceding chapters an account has been given of the 

 main principles on which Biology is based, and of the chief 

 aspects or ways of looking at the subject. We have in the 

 chapters that follow to discuss the subject-matter of Biology, 

 dealing with it in the manner already sketched out. We 

 have seen that progress from lowly organised plants and 

 animals to those of a higher grade in either kingdom, is 

 .marked by what we have termed 'differentiation of parts,' 

 that is by the specialisation or setting aside of special organs, 

 tissues, and cells in the organism for special duties the per- 

 formance of which is necessary for the maintenance of 

 individual and tribal life. It is natural that we should find 

 that the lower we go in the scale of being the less differen- 

 tiation we should meet with, until we ultimately arrive at 

 forms that exhibit no structural or morphological differen- 

 tiation at all, although they do show, as has been pointed 

 out (at page 37), physiological differentiation, or division 

 of labour. In order to understand rightly the principle of 

 differentiation in the higher forms it is necessary that we 

 should study the structure and life-history of one of the 

 simplest types known to us. Such a form is that known as 

 Protamceba primitiva (fig. 6). The utmost that can be said 

 of it is that it is a microscopic speck of almost unmodified 

 protoplasm, presenting at most a differentiation into a denser, 



