222 BIOLOGY 



holophytic; but many plants are holozoic, a condition which is 

 true of all Fungi. 



Protozoa and Protophyta. Both plants and animals may 

 be found among unicellular organisms, the unicellular animals 

 being known as PROTOZOA (Gr. protos = first + zoon = ani- 

 mal), and unicellular plants as PROTOPHYTA (Gr. phyton =' 

 plant) ; see Chapter III. Among such organisms there is some- 

 times a difficulty in distinguishing between animals and plants, 

 since any structure of a distinctive character is lacking. Even 

 here, however, the majority of forms group themselves in 

 one of the two kingdoms, so that they can readily be separated. 

 There are, however, a few forms which prove a puzzle. Euglena 

 (Fig. 29 B), for example, has green chlorophyll, and is thus allied 

 to the vegetable kingdom (holophytic) ; but it has also the power 

 of motion, a mouth, and a red eye-spot. Peranema (Fig. 29 A), 

 however, which is clearly allied to Euglena, has no chlorophyll 

 and no plant characters (holozoic). We may, with equal justice, 

 call both animals or both plants, or perhaps one an animal and 

 one a plant. The bacteria (Figs. 33-35) represent another group 

 which has been difficult to classify clearly; and for many years 

 after they were first studied there was a considerable difference of 

 opinion as to where they belonged. They have a method of 

 life much like that of animals, but their general structure, 

 their multiplication, their division to form long chains, and an 

 occasional formation of spores, are points much more like 

 plants, especially the Fungi. Continued study of the organisms 

 has finally led to the conclusion that bacteria must be regarded 

 as plants rather than animals, associated with the group of 

 Fungi, and considered as resembling yeast and molds. 



A few such organisms as these are the only ones that present 

 much difficulty in distinguishing between animals and plants, 

 and even these can be called animals or plants with a consid- 

 erable degree of certainty. While no sharp line can be drawn, 

 the difficulty of separating them is really not very great, and 

 even among unicellular forms it is rare that we cannot deter- 



