132 



VORTICELLA AND ZOOTHAMNIUM 



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 



//.z. 



FIG. 27. Zoothamnium arlmscula. 



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 (mi), contractile vacuole (c. vac], 

 gullet, and axial fibre (ax.f}. 



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.) 



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

 fission were extended downwards so as to include the dista- 

 end of the stalk, the result would be a branched, tree-like 

 stem with a Vorticella-like body at the end of every branch. 

 As a matter of fact, this process takes place not in Vorti- 



