INFUSORIA. 461 



cule, ■\vliicli enables us to look long at it without wea- 

 riness. 



This last movement is peculiar, and worthy of a 

 moment's closer examination. The stalk, when ex- 

 tended to the utmost, is an elastic glassy thread, nearly 

 straight, like a wire, but never so absolutely straight 

 as not to show slight undulations. The stalk when 

 thus rendered tense by extension, is highly sensitive 

 to vibrations in the surrounding medium ; and as in 

 the circumstances in which we observe the animals, 

 Buch vibrations mnst be every instant communicated 

 to the vessel in which they are confined, the stalks are 

 no sooner tense than they contract with alarm. This 

 depends on a contractile cord which passes throughout 

 the entire len^rth of the stalk, and which is distinctlv 

 visible in the larger species as a narrow band. AVe 

 can scarcely err in considering this ribbon as a rudi- 

 mentary condition of muscle, though we do not recog- 

 nise in it some of the characteristic conditions in which 

 we are accustomed to see it in higher animals. 



The contraction of the muscle is very sudden, ener- 

 getic, and complete. "Willi a rapidity which the eye 

 cannot follow, the vase is brought down almost to the 

 very base of the stalk. Then it slowly rises again, and 

 now we see, what we could not discern in the act of 

 contraction itself, that in that act the stalk was thrown 

 into an elegant spiral of many turns, which at the ut- 

 most point of contraction were packed close on each 

 other, but which in the extending act gradually sepa- 

 rate, and at length straighten their ciirves. 



In any stage of the extension, the sudden contact 

 of the vase with any floating or fixed object apparently 

 causes alarm, and induces the vigorous contraction; 



