V FLAGELLATA I 2 5 



power the rest of the cell is green, owing to the numerous chloro- 

 phyll bodies or chloroplasts. The outermost layer of the 

 cytoplasm shows a somewhat spiral longitudinal striation, 

 possibly due to muscular fibrils. The interior contains many 

 laminated plates of paramylum, and a large single nucleus. At 

 the front of the body at the base of the flagellum is a red " eye- 

 spot " on the dorsal side of the pharynx-tube or pit, from which 

 the flagellum protrudes. "Wager has shown that this tube 

 receives, also on its dorsal side, the opening of a large vacuole, 

 sometimes called the reservoir, for into it discharges the contrac- 

 tile vacuole (or vacuoles). The eye-spot is composed of numerous 

 granules, containing the vegetal colouring matter " haemato- 

 chrome." It embraces the lower or posterior side of the com- 

 munication between the tube and the reservoir. The flagellum 

 has been traced by Wager through the tube into the reservoir, 

 branching into two roots where it enters the aperture of 

 communication, and these are inserted on the wall of the 

 reservoir at the side opposite the eye-spot. But on one of the 

 roots near the bifurcation is a dilatation which lies close against 

 the eye-spot, so that it can receive the light reaction. Euglena 

 is an extremely phototactic organism. It shows various wrig- 

 glings along the longitudinal axis, and transverse waves of 

 contraction and expansion may pass from pole to pole.'' 



Among the Chrysomonadaceae the genus Zooxanthella, Brandt, 

 has already been described under the Eadiolaria (p. 86), in the 

 jelly of which it is symbiotic. It also occurs in similar union in 

 the marine Ciliates, Vorticella sertulariae and Scyphidia scorpaenae, 

 and in Millepora (p. 261) and many Anthozoa (pp. 373 f., 396). 



Of the Chlamydomonadidae, Sphaerella (Haematococcus, Ag.) 

 pluvialis (Fig. 43), and S. nivalis, in which the green is masked 

 by red pigment, give rise to the phenomena of " red snow " and 

 " bloody rain." The type genus, CUamydomonas, is remarkable 

 for the variations from species to species in the character and 

 behaviour of the gametes. Sometimes they are equal, at otlier 

 times of two sizes. In some species they fuse immediately on 

 approximation, in the naked active state ; in others, they encyst 

 on approaching, and unite by the emission of a fertilising tube, 



1 Such movements, permissible by tlie perfectly flexible but firm pellicle, are 

 termed "metabolic" or " euglenoid " in contradistinction to "amoeboid." They 

 also occur in many Sporozoa. 



