406 ann bishop 



5. Food Cycle. 



In Spirostomum ambiguum from a healthy culture 

 numbers of large, round food-balls can be observed throughout 

 the endoplasm. These food-balls may be formed of very small 

 green flagellates, clumped closely tqgether to give them a 

 morula-like appearance ; others are brownish in colour and 

 are composed of compact masses of bacteria. Some large, 

 pink-coloured balls are present owing to the animal having 

 fed upon pink bacteria present in the culture. On one or 

 two occasions I have seen Chilomonads in the endoplasm, 

 enclosed in a large fluid vacuole. That these Chilomonads 

 were not j^et dead was shown by their undulating movements. 

 It is not usual, however, for Spirostomum ambiguum 

 to ingest anything so large. 



In some cultures the food-bodies were entirely bacterial, 

 in others bacteria and flagellates mixed together formed the 

 food-balls, whilst in others the food-balls were composed 

 entirely of green flagellates. The animals were in a flourishing 

 state in all three cases. 



Individual Spirostoma were examined for the presence of 

 fluid vacuoles surrounding the food-balls. In the case of 

 bacterial food-balls lying anterior to, or slightly posterior 

 to, the mouth, distinct fluid vacuoles could be seen encircling 

 them. These vacuoles were absent from balls close to the 

 posterior end. Vacuoles similarly encircled balls of bacteria 

 mixed with flagellates. In the case of flagellate balls, only 

 a very thin film of fluid could be detected, or in many cases the 

 balls seemed to be embedded in the coarsely vacuolated endo- 

 plasm, without the intervention of a vacuole, whatever their 

 position in the animal might be. 



It was soon realized that a definite circulation of the food 

 took place in the endoplasm. An attempt to trace the cycle 

 was made by placing individuals in tap-water for a sufiicient 

 length of time to allow all the food to pass out of the body, 

 and then isolating them in well-slides containing some culture 

 solution rich in green flagellates. Unfortunately all the 



