PHYSIOLOGY OF THE INVERTEBRATA. 21 



lap, for there is no sharp line of demarcation, as far as 

 digestion is concerned, between \\y!d Protozoa and the Bacteria. 

 For instance, if one compares the Gregarine (a parasite) to a 

 bacterium or any other fungus, both forms live by assimilating 

 the products of decomposed organisms, or rather organic 

 matter ; thus showing that the lowest members of the animal 

 kingdom are closely allied to the lowest members of the 

 vegetal kingdom. 



The mode of nutrition among the lowest animals is not 

 uniform — a fact which ought not to appear remarkable when 

 we bear in mind that these animals are made up of all manner 

 of heterogeneous beings that have nothing in common save 

 the microscopic smalluess of their bodies and tlie simplicity 

 of their structure. In the animal kingdom three main types 

 of nutrition may be distinguished : — 



(1) Holophytic or vegetal nutrition. 



(2) Saprophytic or endosmosis nutrition. 



(3) Animal nutrition. 



The first type of nutrition or digestion is found in animal 

 cells that contain chlorophyll, and that nourish themselves 

 by forming assimilable substances from ingredients taken 

 from the medium in which they live. It should be borne in 

 mind that the function of chlorophyll in the animal as well 

 as in the vegetal kingdom is essentially that of nutrition, 

 and not of respiration ; although we shall see later in this 

 volume that many of the animal chromophylls (using the 

 word in its widest sense) have respiratory as well as other 

 functions. 



A large number of the lower animals contain chlorophyll, 

 but these animals are met with chiefly among the Flagcllata. 

 Their assimilative or digestive organs bear the name of chro- 

 matophores. These chromatophores are small granular masses 

 of protoplasm impregnated with a colouring substance. In 

 the centre of the chromatophore is a small bright globule 

 which is said to possess the same chemical reactions as 



