44 THE INVERTEBRATA 



contractile vacuole system, and its reserves are of paramylum. The 

 third is the little group Chloromonadina^ which differs from the 

 Euglenoidina in having oil reserves only and in the delicacy of its 

 pellicle. The orders without groove or gullet are the Vohocina, the 

 most plant-like of the Mastigophora, with green chromatophores 

 (except in a few colourless genera) and starch reserves; and the 

 Chysomonadina, by some regarded as the most primitive members 

 of the class, which have yellow or brown chromatophores and no 

 starch reserves and are often capable of becoming amoeboid. 



Each of these groups exhibits most or all of the varieties of nutri- 

 tion and motility which have been mentioned above. Each of them 

 possesses, (a) coloured, flagellate, solitary forms which constitute 

 most of its membership, (b) coloured species, whose individuals 

 pass most of their time in a non-flagellate condition, as a palmella, 

 which is sometimes of branched, plant-like form, (c) colourless 

 saprophytic forms, and (d) except in the Volvocina, colourless holozoic 

 forms. More than one order has purely amoeboid members, non- 

 flagellate throughout the greater part or all of their existence. The 

 support which this versatility gives to the view that the Mastigophora, 

 and in particular the Phytomonadina, are near the base of the 

 genealogical tree of organisms has already been mentioned. 



Order CHRYSOMONADINA 

 Yellow, brown, or colourless phytomastigina ; without starch reserves, 

 but usually with leucosin and oil ; without gullet or transverse groove ; 

 often amoeboid. 



The genera briefly mentioned under this and the following orders 

 illustrate the range of variety within the group. 



Chrysamoeba (Fig. 38 A, A^). One flagellum; two yellow chromato- 

 phores; no skeleton. Egg-shaped when swimming, but on the sub- 

 stratum becomes amoeboid and may lose flagellum. Ingests food by 

 pseudopodia. In fresh waters. 



Ochromonas (Fig. 38 B). As Chrysamoeba, but with two unequal 

 flagella; and usually one chromatophore. Known to be capable of all 

 three modes of nutrition. 



Dinobryon (Fig. 38 C). Two unequal flagella; two yellow chro- 

 matophores. Secretes a flask-shaped house, which in some species 

 adheres to those of other individuals to form a pseudocolony. In fresh 

 waters. 



Hydrurus (Fig. 38 D-D 2). One flagellum; one chromatophore. 

 Passes most of its life in the resting stage, which by division forms 

 a plant-like growth (see p. 42). In fresh waters. 



Rhizochrysis. Flagella normally lacking ; one chromatophore ; body 

 naked and permanently amoeboid. 



