134 



VORTICELLA AND ZOOTHAMNIUM 



LESS. 



that in the present instance metamorphosis is another means 

 of ensuring dispersal. 



In Vorticella, as we have seen, fission results not in the 



FIG. 26. Zoethamnium arbuscnla. 



A, entire colony, magnified, showing nutritive (n, z) and reproductive 

 (r. z) zooids ; ax. f axial fibre of the stem, 



B, the same, natural size. 



C, the same, magnified, in the condition of retraction. 



D, nutritive zooid, showing nucleus (nit'), contractile vacuole (c. vac), 

 gullet, and axial fibre (ax.J). 



E, reproductive zooid, showing nucleus (nit) and contractile vacuole 

 (c. vac), and absence of mouth and gullet. 



F 1 , F' 2 , two stages in the development of the reproductive zooid. 

 (After Saville Kent.) 



production of equal and similar daughter-cells, but of one 

 stalked and one free-swimming form. It is however quite 

 possible to conceive of a Vorticella-like organism in which 

 the parent cell divides into two equal and similar products, 

 each retaining its connection with the stalk. If this process 

 were repeated again and again, and if, further, the plane of 



