ii BACTERIA 257 



by the process of decomposition into simpler compounds, 

 some of which are diffusible. As the Monad contains no 

 chlorophyll, its nutrition is evidently not holophytic, and, 

 apart from the fact that it possesses neither mouth nor 

 pseudopods, observation seems to show pretty conclusively 

 that it is not holozoic. 



There remains only one way in which nutrition can take 

 place, namely, by absorption of the proteids and other 

 nutrient substances in the solution : the Monad may be 

 said to live immersed in an immense cauldron of broth which 

 it is for ever imbibing, not by its mouth, for it has none, but 

 by the whole surface of its body. This is the saprophytic 

 mode of nutrition, and resembles that which occurs in certain 

 plants which contain no chlorophyll the fungi. It will be 

 seen that the main difference between saprophytic and 

 holozoic nutrition is that in the former digestion, i.e., the 

 process of rendering food-stuffs soluble and diffusible, takes 

 place outside the body, so that constructive metabolism can 

 begin at once. 



In the Monad, the characters are again conflicting (com- 

 pare p. 255) : the probable absence of cellulose, the presence 

 of a contractile vacuole, and the flagella all have an 

 " animal " look, but the mode of nutrition is that of a fungus. 



Decomposition, as already stated (p. 152), is due in the 

 first instance to the action of certain other minute organisms, 

 known as Bacteria, which appear in the earlier stages of the 

 putrefaction of an organic infusion. The nutrition of these 

 organisms, like that of Monads, is usually saprophytic and 

 the movements are generally ciliary ; but as they have a 

 definite cell-wall and no contractile vacuole, they are almost 

 universally classed amongst plants, while Monads are as 

 constantly included in the animal kingdom. 



We see, then, that while it is quite easy to divide the 



PKACT. ZOOL. S 



