iv MOUTH AND GULLET 47 



coloured {(articles were seen to be swallowed in the way 

 described. 



The depression in question is therefore a gullet, and its 

 external aperture or margin (;//) is a mouth. Euglena, 

 like Amoeba, takes in solid food, but instead of ingesting it 

 at almost any part of the body, it can do so only at one 

 particular point where there is a special ingestive aperture 

 or mouth. This is clearly a case of specialization or 

 differentiation of structure : in virtue of the possession of a 

 mouth and gullet Euglena is more highly organized than 

 Amoeba. 



It thus appears that in Euglena nutrition is both holozoic 

 and holophytic : very probably it is mainly holophytic during 

 daylight and holozoic in darkness. 



Near the centre of the body or somewhat towards the 

 posterior end is a nucleus (E, nu) with a well-marked 

 nucleolus, and at the anterior end is a clear space (c. vac) 

 looking very like a contractile vacuole. It has been shown, 

 however, that this space is in reality a non-contractile cavity 

 or reservoir (H, r) into which the true contractile vacuole 

 (c. vac) opens, and which itself discharges into the gullet. 



In close relation with the reservoir is found a little bright 

 red speck (pg) called the pigment spot or stigma. It con- 

 sists of haematochrome (see p. 26) and is curiously like an 

 eye in appearance, so much so that it is sometimes known 

 as the eye-spot. There seems, however, to be no reason for 

 assigning a visual function to it : indeed it has been shown 



O o 



that the greatest sensitiveness to light is manifested by the 

 colourless anterior end of the body. 



As in Haematococcus a resting condition alternates with 

 the motile phase : the organism loses its flagellum and 



