VOETICELLA 11 



C. Eepr eduction, 



1. Fission. The cell-body becomes widened laterally, and a 



constriction appears, running across its distal surface. 

 This constriction extends downwards till it reaches 

 the base of the bell close to the stalk, dividing the 

 cell-body into two halves : of these one is like the 

 parent, and remains attached to the stalk. The 

 other, while still attached to the base of the first, 

 develops a posterior circle of cilia near its base, 

 becomes detached, and swims away by means of the 

 posterior cilia. After a time it attaches itself by. its 

 base to some submerged object, loses its posterior 

 cilia, and forming a stalk by elongation of its base 

 becomes a Vorticella similar to the parent from which 

 it has been cut off. The process of fission may be 

 completed in from one to two hours. 



2. Conjugation occurs sometimes, but it is unlike the con- 



jugation of Paramecium in two important points. 

 Firstly, the conjugation is between two dissimilar 

 forms, an ordinary, large, stalked form, and a much 

 smaller free -swimming form which has originated 

 from repeated division of a large form. Secondly, 

 the union of the two is a complete and permanent 

 fusion, the smaller being absorbed into the larger. 



This permanent fusion of a small active cell with 

 a relatively large fixed cell, followed by division of 

 the fused mass, bears a striking analogy to the pro- 

 cess of sexual reproduction occurring in higher 

 animals. 



3. Encystment may occur after conjugation, and apparently 



as the result of it. The disc becomes retracted ; 

 the cell-body usually separates from its stalk, be- 

 comes spherical, and secretes a cyst around itself; 

 the nucleus enlarges and becomes greatly elongated 

 and then moniliform, and finally breaks up into a 

 number of ' spores.' These are ovoid bodies, each 

 with a circlet of cilia. The cyst ruptures and the 



