THE LARGE GROUP OF rilE SMALLEST OUCXMSMS ir,7 



means of a rotary movement of the Hagelluni, the cell is pulled forward 

 on a spiral course, which is caused partly by the way the flaRellum 

 moves and partly by the irregular shape of the cell. At the same 

 time a current of water is swept into the gullet, bearing with it par- 

 ticles of potential food. The niembranous covering of the bod\- 

 allows the shape of the cell to change, often moving by what is known 

 as euglenoid motion, that is, by a wave of contraction over tlie whole 

 body, thus causing a slow movement like that characteristic of Ameha. 



Although some species of Euglena appear to ingest the food i)ar- 

 ticles that are swept into the gullet, the ordinary nutrition is tiie same 

 as that of a green plant. The imuM- protoplasm of the cell is filletl 

 with chloroplasts (chromatophores) by means of which the raw mate- 

 rials, water, carbon dioxide, and mineral salts, are synthesized into 

 food, thus storing the energy of sunlight. Different species of Euglena 

 are sensitive to different degrees of sunlight and are found to turn 

 towards a source of light, the anterior part of the cell, which contains 

 a red "eyespot," being most sensitive to the light stimulus. When 

 they are exposed to strong sunlight, they change their direction, 

 coming to rest in an area of moderate or "optimum light." Respira- 

 tion is carried on as in any other unicellular form by exchange of 

 gases through the membrane covering the body. During the period 

 when starch is being made in the sunlight enough oxygen is released 

 within the cell body to supply its needs. Excretion of waste products 

 appears to be taken care of by a number of very small contractile 

 vacuoles, that collect fluids from the cell, eliminating them period- 

 ically into a small reservoir which empties into the gullet. The 

 individual cell in some respects acts hke a plant, and in others like an 

 animal. It is a borderline representative, and as such must be 

 regarded as a very primitive organism. 



Reproduction takes place as in other sim])le forms by fission, the 

 free-swimming cell splitting lengthwise*. The si)Iit begins at the 

 anterior end, the two new cells finally having the same structures as 

 are found in the parent cell. In some species of Euglena that encyst, 

 the cell divides by fission during the quiescent period, so that two 

 or more cells are eventually released from the cyst. In some instances 

 as many as 32 have been released from a single cyst. 



Paramecium 



Although protozoa are single cells, some representatives ..f the 

 phylum are much more highly specialized than tiie snnple Ameha. o. 



