74 MANUAL OF ZOOLOGY. 



stricted until complete separation is effected, and then the 

 process differs in no respect from that described as occurring 

 in the fissiparous method of reproduction. 



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 Vorti- 

 celliB. How far this process may be truly sexual is not known, 

 and no form of unequivocal sexual reproduction has hitherto 

 been shown to occur in the case of Vorticella. 



Epistylis is a not uncommon form of fixed Infjisorian 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. lo, 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 caljsx, 

 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, enclosing 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. lo, 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 abdo- 

 minal cavity undergo a constant though slow rotation. 



Carchesium is another form which is like Epistylis in consist- 



