i EUGLENA 35 



times given the special name tractellum. When not swimming the 

 Euglena may often be seen performing curious writhing movements so 

 characteristic in appearance that such movement is termed euglenoid 

 when met with elsewhere. The Euglena is seen to widen itself out about 

 the middle of its length and then the swollen part gradually narrows 

 again towards the two ends. 



The main nutrition of the Euglena is like that of a green plant 

 (" holophytic "), i.e. in the presence of daylight and by means of the 

 green chlorophyll carbon dioxide is split up, the oxygen being set free 

 in the form of bubbles while the carbon is elaborated into a substance 

 termed paramylum almost identical in chemical and physical characters 

 with starch. In Euglenas which have been exposed to light for some 

 time the cytoplasm is crowded with bright shining rods of this substance 

 (Fig. 14, p). In correlation with this mode of nutrition the living Euglena 

 shows a tendency to swim towards the light (" positive heliotropism ") 

 provided it is not too bright. A culture of Euglena in the laboratory 

 contained in a glass trough will gradually concentrate towards the end of 

 the trough nearest the window where the light conditions are at their 

 optimum. 



The Euglena is not entirely restricted to the holophytic type of 

 nutrition. A laboratory culture is found to be benefited by the addition 

 of a little organic food-material in solution and this would appear to 

 indicate that a certain amount of absorption of such food-material can 

 take place through the general surface of the body. 



COPROMONAS 



Copromonas (Fig. 15) is a small pear-shaped inhabitant of fresh water 

 measuring about 16 /* by about 7 ^ or 8 /u. It may usually be obtained 

 in quantity by keeping the contents of the large intestine of a frog or toad 

 in a little water for six or seven days at ordinary room temperature. 

 The shape of the creature is fixed owing to the outer layer of cytoplasm 

 being more condensed and stiffer than is the case with Euglena. Close 

 to the narrower end the surface layer is turned inwards to line a long 

 gradually tapering funnel which as it is used for the ingestion of food 

 we may call the oesophagus or gullet. The single long flagellum (/) 

 projects from the oesophagus and may be traced inwards along 

 its wall to its origin in a deeply staining dot known as the basal 

 granule. Close to this latter there is usually to be seen a reservoir (r) 

 with a small contractile vacuole (c.v). Embedded in the cytoplasm, 

 rather towards the broad end of the creature, is the nucleus (N) 



