PHYTOMASTIGINA 



49 



nu 



amoeboid movement become colourless they are only to be separated 

 from the Sarcodina by certain features (of their nuclei, cysts, swarm 

 spores, etc.) which prove them to be related 

 to various mastigophora. 



Of the orders of the Phytomasttgina, that 

 which contains the most highly organized 

 members is the large and protean group 

 Dinoflagellata, characterized by the posses- 

 sion of two flagella, one longitudinally di- 

 rected and the other transverse, usually in 

 a groove around the body but in a few cases 

 twisted about the base of the longitudinal 

 flagellurrL Three of the remaining orders 

 differ from the rest in the possession, in the 

 anterior part of the body, of a pit ("gullet ") Fig- 37- Lithocircus annu- 

 r 1 • u\u a 11 11 laris. After Lankester. c/)s. 



or groove, from which the flagella usually ^^^^^^^ ^^^^^^^. ^^ /^. 



arise. One of these, the Cryptomonadina, cleus; ^or. pore plate; j^.c. 

 has simple contractile vacuoles and its carbo- "yellow cells ". 

 hydrate reserves are of starch : it is held by 



some authorities to be related to the ancestors of the dinoflagellates. 

 The second, the Euglenoidina, has a more complex 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 Volvocina^ the most plant-like of the Masti- 

 gophora, with green chromatophores (except in a few colourless 

 genera) and starch reserves; and the Chrysomonadina, by some re- 

 garded 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. 



