PROTOZOA : INFUSORIA. 8 I 



attaching themselves to the outside of the calyx of another 

 individual. 



In the third mode of reproduction the Vorticella encysts itself 

 in a capsule, the cilia and pedicle disappear, and the nucleus 

 breaks up into a number of rounded germs, which are ultimately 

 liberated by the rupture of the cyst, and, after a short locomotive 

 stage, develop themselves into fresh Vorticella. How far this 

 process may be truly sexual is not known, and no form of un- 

 equivocal sexual reproduction has hitherto been shown to occur 

 in the case of Vorticella. 



Epistylis is a not uncommon form of fixed Infusorian which 

 is nearly allied to Vorticella, and differs chiefly in the fact that 

 the pedicle is much branched, and is rigid and not contractile. 

 Epistylis (fig. 14, a) usually occurs in the form of a greyish- 

 white nap on the stems of water-plants, or on the head of 

 the common water-beetle, the Dytiscus marginalis. It consists 

 of a plant-like branching and re-branching frond, the stems of 

 which are quite transparent and faintly striated, but are not 

 contractile, though capable of movement from side to side. 

 Each branch of the entire colony terminates in an oval calyx, 

 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, in some species, 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, enclosing the animal. The sarcode-body 

 enclosed 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. 14, b) is inversely conical, and acts as a kind of 

 plug, and it is provided with two tufts of long cilia, one on 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 abdominal cavity undergo 

 a constant though slow rotation. 



Carchesium is another form which is like Epistylis in consist- 

 ing of a number of calyces supported upon a branched pedicle, 



F 



