84 AN INTRODUCTION TO ZOOLOGY 



This in turn enters a large spherical vesicle, the reservoir (r.~), 

 into which several minute contractile vacuoles (A, c. v.) discharge 

 their contents. 



A conspicuous structure in Euglena is the red eye spot or stigma 

 (Fig. 39, A, e.). This is placed near the inner end of the gullet 

 close to the reservoir. It consists of protoplasm in which are 

 embedded a number of granules of hamato chrome. The anterior 

 end of the body of Euglena is said to be more sensitive to light 

 than any other part, and it is supposed by some that the stigma 

 functions as a rather primitive visual organ. This view is made 

 probable by the presence of lens-like paramylum grains just 

 anterior to it. The haematochrome also has many of the charac- 

 teristics of the pigments in the eyes of higher organisms. If 

 kept in the dark, Euglena soon loses its red pigment. A recent 

 view is that the haematochrome shades a sensitive particle of 

 protoplasm. 



Euglena contains a single oval nucleus (Fig. 39, n.) lying in a 

 definite position a little posterior to the center of the body. It 

 has a distinct membrane, and contains a central body which has 

 been called a nucleolus (E), but probably is not, since it functions 

 as a division center during mitosis. 



Euglena derives its green color from a number of oval disks 

 suspended in the protoplasm. These are known as chromato- 

 phores (Fig. 39 A, chr.). They are arranged about a collection of 

 granules situated in the center of the body, and contain chloro- 

 phyll, which is diffused throughout their protoplasmic contents. 

 They manufacture food by a process common in green plants but 

 rare in animals, called photosynthesis (see p. 18 and Fig. 3). 

 The chlorophyll is able, in the presence of light, to break down the 

 carbonic acid (CO 2 ) , thus setting free the oxygen, and to unite the 

 carbon with water, forming a substance allied to starch called 

 paramylum (A and B, am.). If specimens are kept in good light 

 continually, a large amount of paramylum will be stored up for 

 future use, being laid down around some granules of proteid sub- 

 stance near the center of the body. These granules are called 



