THE NUCLEUS OF THE VORTICELL^E. 31 



individual life. They are also capable of becoming 

 encysted^ that is, of secreting a gelatinous cover, 

 and likewise of assuming what Stein calls their 

 Acineta forms, which are usually pear or trumpet- 

 shaped bodies on short stalks, Avith stiff cilia or 

 bristles springing from their heads. Stein thought 

 that their Acineta forms never reproduced their own 

 likeness, but always gave rise to Vorticellids of 

 the original pattern. Other observers have, how- 

 ever, seen young Acinetans developed by old ones, 

 and therefore a part of Stein's theory appears incor- 



Encysted Vorticella, shewing the obliteration of special organs by the advancement 

 of the process. — Pritcha7'd. 



rect. These changes are exhibited in the annexed 

 cuts, which are copied from known authorities. By 

 careful observation of the bodies of Vorticellids, a 

 contractile vesicle may be observed, which appears 

 to cause a movement of fluids, that is probably 

 connected with respiration and the formation and 

 repair of the substance of the animal. It "is placed 

 against the upper part of the alimentary tube." 



Another piece of apparatus in this family, but 

 not confined to it, is the so-called rmclens^ which 



