II NUTRITION 253 



its oxygen evolved, and its carbon combined with the 

 elements of water and used in nutrition. For a long time 

 Euglena was thought to be nourished entirely in this way, 

 but there is a good deal of reason for thinking that this is 

 not the case. 



When the anterior end of a Euglena is very highly 

 magnified it is found to have the form shown in Fig. 69, r. 

 It is produced into a blunt snout-like extremity, at the base 

 of which is a conical depression (a-, s) leading into the soft 

 internal protoplasm : — just the sort of depression one could 

 make in a clay model of Euglena by thrusting one's finger 

 or the end of a pencil into the clay. From the bottom of 

 this tube the flagellum arises, and by its continual move- 

 ment gives rise to a sort of whirlpool in the neighbourhood. 

 By the current thus produced, minute solid food-particles 

 are swept down the tube and forced into the soft internal 

 protoplasm, where they doubtless become digested in the 

 same way as the substances ingested by an Amceba. That 

 solid particles are so ingested by Euglena has been proved 

 by diffusing finely powdered carmine in the water, when 

 the coloured particles were seen to be swallowed in the way 

 described. 



The depression in question serves therefore as a gullet, and 

 its external aperture or margin (;«) as a mouth. Euglena, 

 like Am(.eba, takes in solid food, but instead of ingesting 

 it at almost any part of the bod)', it can do so only at one 

 particular point where there is a special ingestive aperture 

 or mouth. This is clearly a case of specialisation or differ- 

 entiation of structure : in virtue of the possession of a mouth 

 and gullet, Euglena is more highly organised than Amoeba. 



It thus appears that in Euglena nutrition is both holozoic 

 and holophytic (p. 247): very probably it is mainly holophytic 

 during daylight and holozoic in darkness. 



