380 



THE INFUSORIA 



between each contraction were 61 seconds at 5 C., and regularly 

 diminished to 23 seconds at 30 C. In Stylonychia they diminished 

 from 18 at 5 C. to 4 at 30 C. 



DIGESTION. The food of the Ciliata usually consists of minute 

 organisms such as Bacteria, other Infusoria, etc., or particles of 

 organic substance which are able to pass through the mouth into 

 the medulla. As they enter the medullary protoplasm they are 

 accompanied by a globule of water and give rise to the so-called 

 food vacuoles. The food vacuoles pass along a definite course 

 and ultimately reach the anus, or some position in the cortex 

 where a temporary anal aperture can be formed. If a Carchesium 

 (Fig. 27) be fed with finely - powdered food material that 



Fio. 27. 



Diagram of Carchesium to show the 

 course taken by the food vacuoles. 1, 

 the region of ingestion ; 2, of aggrega- 

 tion ; 3, of solution ; 4, ejection. M, 

 the meganucleus. (After Greenwood.) 



Fio. 28. 



Four stages in the food vacuole of a 

 Carchesium fed with white of egg and 

 Indian ink. A, immediately alter in- 

 gestion ; B, first phase of aggregation ; 

 C, second phase of aggregation ; D, just 

 before ejection. (After Greenwood.) 



is stained, the following changes can be observed. Shortly 

 after ingestion the particles are aggregated into a lump at the 

 centre of the vacuole by the centripetal flow of a liquid from the 

 surrounding cytoplasm. A secretion of an acid into the vacuole 

 then occurs and the food particles undergo partial solution 

 (Fig. 28). In the next stage absorption of the dissolved food 

 into the protoplasm takes place, and then the vacuole, with the 

 undigested remnants, travels to the region of the vestibule, where 

 a temporary anus is formed for the discharge of its contents. 



In the mouthless Opalina the food is probably absorbed in a 

 liquid form from the surrounding medium. In some of the 

 TRICHONYMPHIDAE solid food is entangled by the motionless cilia at 

 the posterior end of the body and then enveloped by the proto- 

 plasm in an amoeboid fashion. 



