THE MASTIGOPHORA 



119 



forms that there is apparently good reason for supposing them to 

 play a similar physiological role. In the green flagellates there are 

 often distinct concretions, regarded by some observers as lenses ; and 

 if Pouchet ('86) is correct, a still more striking differentiation is found 

 among the Dinoflagellidia. The so-called eye of Gymnodinium con- 

 sists of a transparent, highly refracting lens, rounded at its free 

 extremity, and always directed forward (Pouchet). The inner sur- 

 face is embedded in 

 a hemispherical, cap- 

 like mass of red or 

 black pigment, which 

 Pouchet considered 

 a choroid. Thelenses 

 develop by the union 

 of from six to eight 

 refringent corpus- 

 cles, while the organ- 

 ism is still encysted 

 or while undergoing 

 fission. The choroid 

 likewise results from 

 the union of several 

 of the pigment gran- 

 ules. Considerable 

 doubt has, however, 

 been thrown upori 

 these observations 

 by subsequent ob- 

 servers. 1 



Other inclusions of 

 interest are the thread-like structures which are common among 

 holotrichous ciliates, and which occur sporadically in other Protozoa. 

 Among the Mastigophora they are found in only two cases {Gony- 

 ostommn Klochmann and Polykrikos Butschli). In the former they 

 are trichocysts similar to those of the ciliate Paramceciiim and allied 

 forms, but in the latter they are true nematocysts, comparable to those 

 of the Ccelenterata. 



Fig. 65. — Sjiiiura uvella Ehr. 

 Each individual of the colony is surrounded by a gelatinous- 

 membrane, and possesses two chromatophores (c) and a nucleus 



B. The FlAgella 



The most characteristic part of a flagellate is its motile organ, the 

 flagellum. This consists of a vibratile filament usually tapering to a 

 fine point, although in some cases {e.g. in all Choanoflagellida) it is 



1 Cf. Penard ('88). 



