The Unicellular Organisms. 



II 



ectosarc, and the rest of the body within this, again, is made 

 up of a more granular and softer protoplasm, the endosarc. 

 The stalk is seen to contain a central core in the shape of 

 a delicately striated filament ; at its attachment to the body, 

 the filament spreads out fan-wise, and forms a layer of ex- 

 cessively fine fibres lying in the ectosarc. This is termed the 

 myophan layer, and is of a muscular nature. It is the muscle' in 

 the stalk which enables the contraction already spoken of to be 

 effected. The figure (Fig. 4) shows the layer plainly. The 

 vorticella possesses a contractile vacuole; this undergoes 



Fig. 5. — Conjugating Vorticellse, highly magnified. (After Maupas.) 

 MAC. NU, macronucleus ; Mic. nu, micronuclei. 



regular expansions and contractions. A nucleus is present, 

 which has a horseshoe form, and near it a smaller body, the 

 micronuckus. The large nucleus is termed the macronucleus. 



Like the amoeba, then, the vorticella is a mass of proto- 

 plasm with a nucleus ; like the amoeba also, the protoplasm is 

 distinguishable into an outer and inner layer, and there is a 

 contractile vacuole; but in other respects the vorticella is 

 more advanced in structure : the ectoplasm is again subdivided 

 into a outer cuticular and an inner layer, below which again is 



