SPIROSTOMUM AMBIGUUM 407 



animals treated in this way refused to feed. After many 

 unsuccessful attempts a few animals were persuaded to feed 

 from such a culture solution in small test-tubes. 



The food is wafted down the long peristomial groove to the 

 cytostome by the peristomial membranellae. At the base of 

 the cytostome the food is gathered into a sphere, which varies 

 considerably in size from a ball only just visible under the 

 I" objective, to one-half the width of the animal's body. The 

 food-ball then passes forward towards the anterior end of 

 the body. Its movement is, comparatively speaking, rapid. On 

 reaching the anterior end of the body it moves to the posterior 

 end in a course parallel to its former one. After regaining 

 a position approximately level with the cytostome its progress 

 becomes much slower, and with many halts it passes down the 

 side of the contractile vacuole, along the narrow strip of endo- 

 plasm found in this region, to the cytopyge. This cytopyge 

 appears at the base of a slight depression situated in the middle 

 of the posterior end. The undigested material is evacuated 

 slowly, one sphere at a time. 



Since the movement of the food-balls at the posterior end 

 of the animal is so slow, there is often an accumulation 

 of these spheres in the neighbourhood of the contractile 

 vacuole. 



The course followed by flagellate or bacterial food-bodies 

 is shown in Text-fig. 4. 



In order to discover whether the course taken by food-balls 

 was similar in the case of substances of no food value, animals 

 were taken straight out of the culture and put directly into a 

 suspension of finely powdered carmine in culture solution. The 

 particles of carmine were wafted to the cytostome. The granules 

 of carmine were collected at the base of the cytostome exactly 

 as were the bacteria in the cases cited above, but the carmine 

 grains were packed much more loosely together. Like the 

 bacterial balls, the carmine balls moved from the base of the 

 cytostome forward, but instead of passing right to the anterior 

 end they passed inwards, as shown in Text-fig. 3, and then 

 continued backwards down the opposite side of the body to 



B e 2 



