48 THE INVERTEBRATA 



very rich in organic matter the chromatophores grow pale and shrink 

 even in the Ught, and in the dark this happens even with a low per- 

 centage of such substances. It has not been established that Euglena 

 uses its gullet to take solid food. Fresh waters, and infusions. 



Peranema (Figs. 11, 39 E). Without chromatophores; gullet sup- 

 ported by rods and can open or close. Saprophytic and holozoic. 

 Paramylum reserves formed. In infusions. 



Copromonas (= Scytomonas, Fig. 39 F, F'). Without chromato- 

 phores; body pear-shaped; no metaboly; gullet long and narrow. 

 Nutrition holozoic, chiefly by bacteria. Coprozoic in dung of frogs. 

 After some days of binary fission syngamy takes place between 

 ordinary. individuals (hologamy), the nuclei first throwing out two 

 "polar bodies". Some zygotes encyst; others continue to divide. 

 Finally all encyst. The cysts are washed away and swallowed by a 

 frog or toad with its food. They pass uninjured through the gut and 

 hatch in the moist faeces, where alone the active stage exists. 



Colacium. Normally in the palmella phase, forming branched, 

 plant-like growths. 



Order CHLOROMONADINA 



Phytomastigina which have numerous green chromatophores or 

 are colourless ; with reserves of oil ; gullet ; and complex contractile 

 vacuole ; without transverse groove ; possessing a delicate pellicle, or 

 amoeboid. 



Vacuolaria. Typical, bright green members of the group, which 

 pass much of the life history in the palmella stage. In fresh waters. 



Order DINOFLAGELLATA 



Phytomastigina which have numerous yellow, brown, or green 

 chromatophores or are colourless; with reserves of starch or oil or 

 both; with complex vacuole system; with two flagella, one directed 

 backwards and usually in a longitudinal groove (sulcus) and the other 

 transverse, usually in a more or less spiral groove (annulus) ; usually 

 with an armour of cellulose plates, but sometimes amoeboid. 



The complex vacuoles of dinoflagellates are not, as was held, con- 

 tractile, but contain water driven into them through their external 

 pores by the action of the flagella. Their function is unknown. 

 Possibly they are hydrostatic, or alimentary, or both. 



The plane of fission is oblique, but resembles the longitudinal 

 fission of other Mastigophora in passing between the two flagella. 

 Fission may be within or without a cyst: in either case it may be 

 simply binary or repeated ; within a cyst it is sometimes multiple. The 

 products of repeated binary fission of pelagic forms sometimes hang 



