VORTICELLA 1 1 



with the deeper, ' myophan,' layer of the ecto- 

 sarc of the body. The spiral shortening of the 

 stalk, is due to its contraction. In a specimen in 

 which this band had been broken, it was seen to 

 be drawn up suddenly towards the body at each 

 inversion of the disc, the stalk, however, remaining 

 straight. 



2. The endosarc is the more fluid granular central portion 

 of the cell-protoplasm. It does not extend into the 

 stalk. 



a. The food vacuoles circulate with the endosarc. 



b. The nucleus is an elongated curved band in the 



upper part of the body near the pharynx. 



c. The single pulsating vacuole is spherical, and 



situated between the disc and the vestibule, into 

 which latter it opens. 



G. Beproduction. 



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 

 ceU-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 an aboral circle of cilia near its base, 

 becomes detached, and swims away by means of the 

 aboral cilia. After a time it attaches itself by its- 

 base to some submerged object, loses its aboral 

 cilia, and forming a stalk by elongation of its base 

 becomes a VorticeUa 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 unhke 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 



