CILIATA. 39 



trichocysts are sometimes present in the cortical plasma. It 

 appears that on suitable stimulation they have the power of everting 

 needle-shaped structures which probably have a stunning action 

 upon other organisms. In one form, Epistylis umbellaria, dcjimte 

 nematoeysts, like those of the Coclenterata, are present in the 

 ectoplasm. 



The contractile vacuoles are fixed in position and contained in the 

 ectoplasm, generally near the surface of the body. When more than 

 one is present they increase in number with the size of the individual. 

 They open outward through pores in the pellicle, or in some cases 

 (Vorticellines) into a reservoir, or there may be a long excretory 

 canal as in Lemladion. The contractile vacuoles are re-formed by 

 the fusion of formative vacuoles which appear in the neighbouring 

 plasma during the diastole of the preceding vacuole, or there may 

 be canals leading even from distant parts of the 

 body, which collect the fluid for the formation 

 of the new vacuole (Paramcecidce). The walls 

 of these canals are, in some cases at any rate, 

 contractile. These vacuoles and canal -systems 

 are probably excretory in function, collecting 

 waste matters in solution from the body gener- 

 ally and discharging it externally. They have 

 been compared, probably with some justice, to 

 the excretory organs of Platyhelmintlies and 

 Rotifer a. 



The vibratile appendages of the body are of FlG - w.-CMiodon cucui- 



, , . , j A. *, after Stein; with 



four kinds, and they all seem to be processes rod -apparatus round 

 of the cuticle or alveolar layer. the oesophagus. N 



si\ m .4 -T 1-1 * nucleus; excreta are 



(1) I he nne cilia which serve for swimming. passing out per anum. 



(2) The Cirri : stouter vibratile processes 



which taper towards their free ends. They are placed on the ventral 

 surface of the body, and serve for locomotion in a pediform manner 

 (hence called legs or styles), or for attachment. 



(3) Membranellse : short flattened cilia which, when ending in a 

 point, are not clearly distinguishable from cirri; they form the 

 adoral zone of the peristome of the fyrirotricha, in which they create 

 the whirlpools by which the food is brought to the mouth. 



(4) Undulating membranes placed in the neighbourhood of the 

 mouth, and assisting in the prehension of food. 



The fibre which can often be made out running from the base of 

 the cilium, apparently to the myophane layer, is continuous with the 



