284 BIOLOGY OF THE PROTOZOA 



of the cell is highly characteristic of several species (Euglena trip- 

 ten's, FjVcjJena oxyitrls, Euglena spiroides, Phacus longiccmda, etc.). 



The majority of Euglenida possess a definite cytostome from the 

 base of which a flagelliim emerges (Urceolus, Scytomonas, etc.). 

 In Entosiphon a protriisible tube runs deep into the endoplasm. 

 Defecation areas are also present in Euglenopsis and Anisonema. 



Flagella of the Euglenida afford the best material for the study 

 of this type of motile organ. They are frequentl;^' large and show 

 the axial fibril and the elastic sheath with great clearness. The 

 majority of forms have only one but two are not uncommon. If 

 two are present they may be of equal length and directed forward 

 (Evtreptia) or one may be accessory and "\'ery short (Di stigma, 

 Sphen())ii()nas) or drawn out into a long trailing flagellum (Noto- 

 solenus, Anisonema, Tropidoscyj^hns, Heteronema, EntosipJion, etc.). 



A complex vacuole system is characteristic. This consists of a 

 reservoir with canal opening into the cytostome and one, two or 

 more contractile vacuoles surrounding the reservoir and emptying 

 into it. 



Chromatophores are present in Euglenidse but absent in the 

 other two families. They are usually discoid, cup-shape, band-form 

 or stellate in shape and may or may not contain pyrenoids. They 

 normally form green chlorophyll in the light, or the green color 

 may be masked by hematochrome (karotin). 



Reserve products of nutrition in the form of paramylum and oil 

 are also characteristic. The former apparently increase and 

 decrease in size according to the activity and environment of the 

 cell; these are quite diverse in form but the same type is apparently 

 invariable in the same species, hence they form a suitable means of 

 diagnosis for different species. Stigmata likewise, are common in 

 the Euglenida although they may also be present in colorless Euglen- 

 ids (e. g.. Astasia oceUata, Khawkine, Euglena quartana, Moroff). 



Of the three families Euglenidae, Astasiidfe, and Heteronemidse, 

 the first is more commonly represented b\' fresh-water species. 

 They occur in all waters, Astasiida? and Heteronemidte more in 

 infusions and in stagnant pools. Very little reason is to be found 

 for distinguishing a separate family Peranemidje from the Astasi- 

 idae while colorless forms with two flagella are included in the present 

 family Heteronemidee. 



Family 1. Euglenidse, Stein.— Medium-sized organisms of spindle 

 shape or flattened form and with widely distributed tendency to 

 metaboly. The majority have spiral striations or twisted body. 

 Flagella usually 1 in number, (2 in Evtreptia), emerge from the 

 cytopharynx. Chromatophores generally present but may be 

 absent in questionable forms (Euglena quartana); similarly with 

 stigmata, while paramylum and oils are usiuxlly present. In one 

 genus (Ascoglena) the cell occupies an attached gektinous cup. The 



