158 ELEMENTARY ZOOLOGY. 



are colonial; that is, they do not separate when they divide, but 

 each daughter develops a stalk and remains attached to the main 

 stem (Fig. 39, B). 



175. Euglena. This form is found under much the same condi- 

 tions as ameba. Occasionally it is seen in great numbers making 

 a thin scum on ponds, in very warm weather a short time after a rain. 

 It is remarkable in that it has the green coloring matter of plants 



FIG. 38. Paramecium in optical section (semi-diagrammatic). A, anterior end; 

 c, cilia; ec, ectosarc; en, endosarc; f.v., food "vacuole"; g, gullet; N, meganucleus; n, 

 micronucleus; o, groove leading to mouth; p.v., pulsating vacuoles in different stages 

 of contraction; v, a food vacuole in process of formation. 



Questions on the Figure. How do the anterior and posterior ends 

 differ? Compare with other protozoa in this respect. What is 

 there to convince one that this is a single-celled animal? Is it 

 more or less highly "organized" than the other protozoa of which 

 you can find figures? To what division of Protozoa does Para- 

 mecium belong? 



and the motile condition of animals (Fig. 40, A). It differs from the 

 ameba in that it has a wall, and has a single long lash (flagellum) 

 extending from the mouth, which is a permanent opening in the 

 cell wall. The flagellum enables the animal to lash its way through 

 the water; it also aids in carrying food back to the mouth. There 

 is a large rounded nucleus, and a peculiar red spot ("eye-spot") 

 just back of the mouth. 



176. The Spore -animals. We usually think of plants alone as 

 producing spores, but there is one group of the Protozoa whose 



