IV MOUTH AND GULLET 47 



coloured particles were seen to be swallowed in the way 

 described. 



The depression in question is therefore a gullet, and its 

 external aperture or margin (w) is a month. Euglena, 

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

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

 particular i)oint 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 well-marked globular nucleus (e, nu), 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 pigmefit 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 often known as the 

 eye-spot. Recent experiments seem to show that it is 

 specially sensitive to light and is therefore a true eye in the 

 sense of a light -perceiving organ although having no actual 

 visual function. 



As in Haematococcus a resting condition alternates with 

 the motile phase : the organism loses its flagellum and 



