34 



PROTOZOA. 



generally present, and contain chlorophyll and diatomin*; but there 

 are colourless forms. Amylum, fat, red pigment, and stigmata may 

 also be present. There is always a longitudinal groove upon what we 

 call the ventral surface, and in the Dinifera there is a second groove 

 the transverse groove encircling the body ; the latter generally 

 has a slightly spiral course (so that the two ventral ends of it are 

 not quite at the same level, Figs. 27, 28) and in one genus makes 

 two complete turns. The two flagella arise, as a rule, close together, 

 where the two grooves cross one another. The transverse flagelluni 

 lies wrapped round the body in the circular groove. The flagella 



project through a hole in the cuticle, 

 which in some genera at least ex- 

 tends as a slit along the left side of 

 the ventral groove, being enlarged 

 posteriorly where the longitudinal 

 flagelluni projects. Reproduction 

 takes place by transverse fission. 

 Conjugation has been observed in 

 a few forms, and in a few cases 

 individuals have been observed to 

 unite in chains (*? a form of conju- 

 gation). In PolyfcriJcos, which has 

 four nuclei, there are eight trans- 



FIG. 28.-Shell of Ceratium tripos (after verse ^OWS, each with a flagelluni. 



stein), if longitudinal furrow ; q f The presence of a mouth is doubtful. 



transverse furrow. ^ , 



resli- water and marine. 



Sub-order 1. ADINIDA. 



Longish bilaterally -symmetrical forms with inclination to asymmetry ; the 

 two flagella arise at the anterior pole, and the transverse furrow is not developed ; 

 with bivalved porous membrane ; two vacuoles near one another at the anterior 

 end ; chromatophores. 



Fam. 1. Prorocentrina, with characters of sub-order. Exuviaella Cienk. ; 

 Prorocentrum Ehrb. 



Sub-order 2. DINIFERA. 



With a more or less distinct transverse furrow containing a flagellum. Longi- 

 tudinal flagelluni directed backwards. 



Fam. 2. Peridinida, with the transverse groove at or near the centre of the 

 body. Podolampas Stein ; Peridinium Ehrb. ; Goniodoma Stein ; Ceratium 

 Schrank (Fig. 28) ; Fyrophacus Stein ; Glenodinium Ehrb. (Fig. 27) ; Gymno- 

 dinium Stein, without cuticle ; Ceratocorys Stein. 



* By some naturalists there is supposed to be affinity between the Dino- 

 flagellata and the silicious Algfe, the Liatomaccce. 



