VORTICELLA. 17 



sarc is more definite than it is in Amoeba or Paramoecium. 

 The ectosarc is uniformly granular, and it contains no food 

 vacuoles, oil-drops, or foreign bodies. 



3. The ectosarc, like the endosarc, is in constant motion ; 

 but, oAving to the absence of large particles, the currents 

 :irc very hard to discover. They flow in an opposite di- 

 rection to those of the endosarc. 



4. The longitudinal striations are restricted to the 

 outer surface of the ectosarc, which is thus divided into a 

 superficial muscular or contractile layer (Fig. 5, 6), and 

 a deeper unspecialized layer, (Fig. 5, c). The two are 

 not sharply separated. 



5. The contractile axis of the stem is a continuation of 

 the contractile layer of the ectosarc. Its upper end is dis- 

 tinctly striated or divided into a series of parallel, dark- 

 colored transverse bands, separated from each other by 

 mere transparent spaces. 



c. The transparent, elastic cuticle (Fig. 4, ?, and 

 Fig. 5, a) covers the whole outer surface, and is thin 

 upon the disc and peristome ; thicker upon the bell, and 

 thickest in the stem. A very high power shows that its 

 surface is sculptured by parallel rows of fine dots. The 

 loose spiral, formed by the contractile axis of the stem, is 

 attached to the cuticle only on one side ; and when the axis 

 contracts the tubular cuticle is thus thrown into a spiral, 

 by the flattening of which the animal is drawn back to its 

 point of attachment. AYhen the contractile axis relaxes, 

 the elasticity of the cuticle straightens the stem, and 

 pushes out the body of the animal. When the peristome 

 and disc are retracted, the cuticle folds in with them, and 

 its elasticity causes the body to expand as soon as the 

 force is relaxed. The rapid contractions of the animal are 

 thus due to the contractile power of the outer layer of 



