THE ALGAE 



53 



.a 



Canal ■ 

 Reservoir 



Paramylon 

 grain 



Nucleus 



spirally striated membrane. The upper or anterior end of the organism is 

 rounded, and slightly to one side is an indentation into the protoplast, leading 

 to a canal through which passes 

 out a single flagellum about as 

 long as the body of the organism. 

 At the base of this canal lies a large 

 vacuolar reservoir which has a 

 thickening at its upper end which 

 may act as a sphincter for opening 

 and closing the canal. Near the 

 reservoir are one or more pulsating 

 vacuoles which may fuse with, or 

 in any case discharge their con- 

 tents into, the reservoir. Adjacent 

 to the reservoir is a prominent red 

 eye spot which has been shown to 

 be light-sensitive. 



The nucleus (Fig. 29) occupies 

 a posterior position. It is sur- 

 rounded by a colourless area of 

 cytoplasm. The chlorophyll is 

 contained in a series of about ten 



rod-like chloroplasts which radiate out from the centre of the cell. 

 Each chloroplast has, at the end nearest the centre, a group of large 

 solid granules of paramylon of very diverse shapes. These grains actually 

 develop in the cytoplasm but come to lie attached to the inner ends of the 

 chloroplasts. Paramylon is a polysaccharide allied to starch. It differs, 

 however, in giving no colour with iodine, and it is not attacked by the enzyme 

 diastase. 



A few species of Eiiglena are devoid of chlorophyll. Some live as sapro- 

 phytes, even in the intestines of animals, such as frogs and tadpoles, while a 

 few have been described as capable of ingesting solid food material. 



The organisms are all capable of active movement, swimming by the lash- 

 ing of the flagellum and the corkscrew-like turning of the whole body. They 

 also perform a characteristic, rhythmical and contractile motion, termed 

 euglenoid movement. The flagella show an axial thread with a protoplasmic 

 sheath, and there are indications that the axial thread itself consists of a 

 spiral strand of still finer fibres. 



Fig. 28. — Euglena viridis. Stained preparation 

 showing nucleus and paramylon grains. 



Reproduction 



Reproduction is effected by the longitudinal division of the body into two. 

 This is called binary fission. In most instances the individual comes to rest, 

 secretes an envelope of mucilage, and then proceeds to divide, beginning at 

 the front end of the protoplast. In some species the cells so formed may 

 round themselves off and divide again and again, so that a large number of 



