260 



THE PROTOZOA 



dition, with a backwardly-directed trailing flagellum (" Schlepp- 

 geissel"), deserves special attention, since by attachment of the 

 trailing flagellum to the body an undulating membrane (p. 56) 

 may arise ; and that it has actually so arisen in some cases is 

 indicated by the existence of pairs of similar forms, in which a 



FIG. 110. Codonosiga botrytis. A, Young specimens 

 attached singly to the stalk of a Vorticella ; B, colony 

 of six individuals on a common stalk ; C, stalked 

 individual which has recently divided into two, pro- 

 ducing a dichotomous division of the stalk, c.v., 

 Contractile vacuole. After Stein. 



trailing flagellum, free from the body, in the one form is represented 

 by the marginal flagellum of an undulating membrane in the 

 other as, for example, Trichomastix and Trichomonas (Fig. 5) , 

 Prowazekia (Fig. 141), and Trypanoplasma (Fig. 36). 



In one group of flagellates hence known as the Choanoflagellata 





