NUTRITION 123 



flagella cannot be considered as definitely established. It may also be 

 open to question if the granules in which they originate, and which are 

 generally styled blepharoplasts, are actually of this nature. 



PHYSIOLOGY OF THE PROTOZOA. 



Many of the physiological processes which regulate the life of Protozoa 

 have been referred to above. It will only be necessary to review these in 

 a general manner under the headings Nutrition, Movement, Reaction to 

 Stimuli, Influence of Environment, Influence of Syngamy. 



NUTRITION.— The essential food requirements of Protozoa are those of 

 living matter in general. There is a constant expenditure of energy, 

 necessitating a continuous supply of nourishment, which includes oxygen, 

 simple chemical compounds, more complex organic substances, or highly 

 organized proteid materials. Oxygen is an essential requirement, as it is 

 of all living matter, but the method by which it is obtained varies, as it 

 does between the vegetable and animal kingdoms. There are no special 

 organs of respiration, so that absorption of oxygen and discharge of carbon 

 dioxide takes place by a process of diffusion through the surface of the 

 body. Certain Protozoa, like plants, possess chromatophores, and by 

 means of their pigments or chromophyll are able, in the presence of sun- 

 light, to obtain oxygen from the carbon dioxide which is in solution in 

 the liquids in which they live, or which is formed by the organism itself. 

 The chromatophores, which are green when they contain chlorophyll or 

 red when the pigment is haematochrome, multiply by binary fission, as do 

 also certain refringent granules called pyrenoids which they contain. 

 They behave in many respects as independent organisms, and this has 

 given rise to the view that they may be actually organisms living in a 

 condition of symbiosis with the cells in which they occur. This method of 

 nutrition is described as being holophytic, in contrast to the holozoic type, 

 which is characteristic of Protozoa, which are devoid of chromatophores, 

 and which must of necessity absorb oxygen directly from the liquid in 

 which they live. In either case the organisms require oxygen, so that the 

 two types of nutrition, the holophytic and holozoic, do not imply any 

 essential difference in the character of the protoplasm of which their bodies 

 are composed. This is well illustrated by certain species of Euglena, which 

 normally have chromatophores, and lead a holophytic mode of existence 

 (Fig. 6). Under certain conditions, as when cultivated in the dark with 

 consequent loss of the pigment, they behave as organisms devoid of 

 chromatophores. The holophytic forms nourish themselves like plants, 

 and, in addition to the power conferred on them by the coloured pigments 

 of being able to utilize carbon dioxide for the purpose of acquiring a supply 



