PROTOZOA : INFUSORIA. 63 



articulated to the stem by a distinct joint, upon which it can 

 move from side to side. The calyces are oval or somewhat 

 campanulate, but have the power of altering their dimensions, 

 and especially of contracting so as to shorten their antero- 

 posterior diameter. Each calyx terminates distally in a 

 slightly elevated annular aperture, the margins of which are 

 regularly toothed. The calyx appears to be formed by a 

 hardening of the cuticle, and to form a distinct case, with a 

 double margin, inclosing the animal. The sarcode body en- 

 closed within this outer envelope is of a light brown colour 

 and full of minute granules, with larger food-vacuoles and a 

 well-marked contractile vesicle, which contracts and dilates 

 two or three times a minute. The animal can retract itself 

 entirely within its cup, and can at will exsert a ciliated disc, 

 This disc (fig- 10 5) is inversely conical and acts as a kind of 

 plug, and it is provided with two tufts of long cilia, one 011 

 each side. On one side of the protrusible disc is the oral 

 aperture, which is continued by a distinct and well marked 

 gullet into a central ill-defined cavity. Both the entrance of 

 the gullet and the bottom of the central cavity are provided 

 with very long, actively vibrating cilia, some of which are 

 almost setiform. The entire granular contents of the abdo- 

 minal cavity undergoes a constant though slow rotation. 



Garchesium is another form which is like Epistijlis in con- 

 sisting of a number of calyces supported upon a branched 

 pedicle, but differs from Hpistylis and agrees with Vorticella in 

 the fact that the pedicle is contractile. 



Stentor, or the trumpet-animalcule, is another common In- 

 fusorian which is closely related to Vorticella. It consists of a 

 trumpet- shaped calyx, devoid of a pedicle, but possessing the, 

 power of attaching and detaching itself at will. When de- 

 tached it swims by means of the anterior circlet of cilia, just 

 as the calyx of Vorticella will, if broken from its stalk. In 

 Vaginicola the essential structure is much the same as in 

 Vorti,cella, but the body is protected by a membranous or horny 

 case (' carapace ' or ' lorica ') within which the animal can 

 retire. 



Amongst the structures of the Infusoria which require some 

 notice, are the 'pigment spot' and the 'tricho-cysts.' The 

 pigment spot is a brightly coloured solid particle, generally, 

 red, of very common occurrence in many Infusoria, but of 

 quite unknown function. The * tricho-cysts ' are vesicular 

 bodies, capable of emitting thread-like filaments, and greatly 

 resembling the urticating cells of many of the Goclent^ratu . 

 They have been detected in Bursaria, as well as in other 

 members of this order. 



