CILIATA 1 47 



For some time no change is shown in the food-material itself : 

 this is the stage of " storage." Eventually a fresh zone of liquid, 

 the true digestive vacuole, forms again round the food-pellet, and 

 this contains a peptic juice, of acid reaction. The contents, so 

 far as they are capable of being digested, liquefy and disappear. 

 Ultimately the solid particles in their vacuole reach the anal 

 area of the vestibule, and pass into it, to be swept away by the 

 overflow of the food-current. The anus is seated on a transverse 

 ridge about a third down the tube, the remaining two -thirds 

 being the true pharynx. 



Fission is usually transverse ; but is oblique in the conical 

 Heterotrichaceae, and longitudinal in the Peritrichaceae. It in- 

 volves the peristome, of which one of the two sisters receives the 

 greater, the other the lesser part ; each regenerates what is missing. 

 When there are two contractile vacuoles, as in Paramecium, 

 either sister receives one, and has to form another ; where there 

 is a canal or reservoir divided at fission, an extension of this 

 serves to give rise to a new vacuole in that sister which does not 

 retain the old one. In some cases the fission is so unequal as 

 to have the character of budding (SpirocJiona). We have de- 

 scribed above (p. 144) the relations of the nuclear apparatus in 

 fission. 



Several of the Ciliata divide only when encysted, and then 

 the divisions are in close succession, forming a brood of four, 

 rarely more. This is well seen in the common Colpoda cucullus. 

 In the majority, however, encystment is resorted to only as a 

 means of protection against drought, etc., or for quiet rest after a 

 full meal (Zacrymaria). 



Maupas^ has made a very full study of the life-cycles of 

 the Ciliata. He cultivated them under the usual conditions 

 for microscopic study, i.e. on a slide under a thin glass cover 

 supported by bristles to avoid pressure, preserved in a special 

 moist chamber ; and examined them at regular intervals. 



The animals collect at that zone where the conditions of 

 aeration are most suitable, usually just within the edge of the 

 cover, and when well supplied with food are rather sluggish, not 

 swimming far, so that they are easily studied and counted. 

 When well supplied with appropriate food they undergo binary 

 fission at frequent intervals, dividing as often as five times in 

 1 Arch. Zool. Exp. (2) vi. vii. 1888 1889. 



