DINOFLAGELLATA. 33 



individuals may be naked, or may secrete a cup, or may be .embedded 

 in jelly (Proterospongia). Their nutrition is holozoic. The food- 

 particles, brought by the currents set up by the flagellum, adhere 

 to the outer side of the collar, down which they move untif>they 

 are swallowed by a kind of vacuole-like elevation of the body proto- 

 plasm at the base of the collar (oral vacuole). Ejection of faecal 

 matter takes place in the collar area, though there is no distinct 

 anal spot. The collar is protoplasmic and retractile. 



Fam. 1. Phalansterina. Colonial, each individual in a granular gelatinous 

 tube. Colonies either a lamellar expansion or a dichotomously branching stock ; 

 collars narrow, conical, and of constant shape. Phalansterium Cienk. 



Fam. 2. Craspedomonadina. Solitary or colonial, collars considerable, conical 

 and of changeable form. Individuals naked or with incomplete cup, or in 

 gelatinous mass. Monosiga Kent ; Codosiga J. Clark (Fig. 26) ; Codonocladium 

 Stein ; Hirmidium Perty ; Proterospongia Kent, colonial, the individuals are 

 embedded in jelly and readily assume the amoeboid condition ; Salpingosca 

 J. Clark, and Polyceca Kent, with thin-walled cups. 



Order 3. DINOFLAGELLATA.* 



Bilateral, asymmetrical Mastigophora with a ventral groove and 

 two flagella. A membrane consisting of cellulose is generally 

 present. 



The Dinoflagellata are most nearly allied to the Cryptomonadina. 

 Like these they possess two flagella, which 

 arise from a groove. The flagella are always 

 distinguishable from one another: the one 

 as the longitudinal flagellum directed forwards 

 (Adinida) or backwards (Dinifera), and the 

 other as the transverse flagellum because it has 

 a transverse circular course round the base of 

 the first (Fig. 27). The transverse flagellum 

 moves by very short waves, and was until lately 

 taken to be a transverse ring of fine cilia (hence FiG.27-Gien^Uniumcinc- 



tum (after Butschli) ven- 



Ciliojiagellata). A membrane or shell consisting trai view, g longitudinal 

 of cellulose and often prolonged into processes gSSlVSS! 

 (Fig. 28), is nearly always present. They closely OG stigma (eye -spot); 

 resemble the Flagellata in their internal struc- 

 ture. Except in one genus (Polykrikoe), there is never more than 

 a single nucleus. Chromatophores of a green to brown colour are 



* R. S. Bergh, "Der Organismus der Cilioflagellaten. " Morph. Jahrb., 7, 1881. 

 Fr. Schiitt, "Die Peridineen d. Plankton-Expedition," Th. 1. Ergeb. Plankton- 

 E\p., 4, 1895. 



