FLAGELLATA 



131 



show variability as to their nutrition, wiiich is soniotinies 

 holozoic. Uiuler these conditions tlie cell can take in food- 

 particles as bulky as the eggs of Eotifers and Copepods, by the 

 protrusion of a pseudopod at the junction of the two grooves. 

 As in most coloured forms an eye-spot is often present, a cup- 

 shaped aggregation of pigment, witli a lenticular refractive body 

 in its hollow. A contractile vacuole, 

 here termed a " pusule," occurs in 

 many species, communicating with 

 the longitudinal groove by a canal. 

 Xematocysts (see p. 246 f.) are 

 present in Pohjkrilcos, trichocysts '^''■' 

 (see p. 142) in several genera. 



Division is usually oblique, 

 dividing the body into two dis- 

 similar halves, each of which has 

 to undergo a peculiar growth to 

 reconstitute the missing portion, 

 and complete the shell. The in- 

 complete separation of the young 

 cells leads to the formation of 

 cliains, notably in Ceratiimi and Fic 

 PolykrilMS, the latter dividing 

 transversely and occurring in 

 chains of as many as eight. The 

 process of division may take place 

 when the cell is active, or in a cyst, as in Fyrocystis (Fig. 47). 

 Again, encystment may precede multiple fission, resulting in 

 the formation of a brood of minute swarmers. It has been 

 suggested that these are capable of playing the part of gametes, 

 and conjugating in pairs.^ 



The Dinofiagellates are for the most part pelagic in habit, float- 

 ing at the surface, and when abundant tinge the water of fresh- 

 water lakes or even ponds red or brown. Feridinium (Fig. 46) 

 and Ceratiuvi (the latter remarkable for the horn-like backward 

 jirolongations of the lower end) are common genera both in the sea 



I'cikUnium divergens. a, 

 Flagellum of loiigitiulinal groove ; 

 b, tlagelluiu of transverse groove ; 

 <•/•.(•, contractile vacuole surrounded 

 by fouiuuive vacuoles ; n, nucleus. 

 (After Scliiitt.) 



^ Conjugation of adults has been observed by Zederbauer {Bcr. Deutsch. Gcs. 

 x.\ii. 1904). A sliort connecting tube is formed by tlie meeting of outgrowths 

 from either mate ; their protoplasmic contents meet and fuse herein to form a 

 spherical resting-spore, as in tiie Conjugate Algae. 



