160 NATURAL HISTORY 



its delicate body : when disturbed, it can withdraw itself 

 entirely within the case ; at other times it is protruded, 

 and the cilia occasion a current towards it, w^hereby it 

 procures its food. In some specimens the shell is elon- 

 gated, and appears like the Trichoda ingenitay and occa- 

 sionally two are observed in the same case, as at figure 

 236*5 which indicates that they propagate by scission. 

 It would be an interesting subject to ascertain how the 

 shell is formed, and whether it can be reproduced, as I 

 have sometimes discovered them without the animal. 

 They are found among confervse, and attached to the 

 exuvia of insects. 



388. VoRTicELLA operculuria. — The covered Vorticella 

 appears, from the description of Mr. Anderon, to be en- 

 closed in a crustaceous sheath, with the upper part or lid 

 moveable, as shewn in the drawing, figure 248. This lid 

 or cover is surrounded with cilia, and it is connected to 

 the interior of the bell by a long muscular cord : by 

 means of the cilia it commands a wide range for pro- 

 curing its food, but it retires on the slightest disturbance : 

 in this state it does not appear that Mr. A. observed the 

 cilia. 



389. Vorticella berherina is shewn at figure 249, 

 magnified. The bell is capable of withdrawing the stem 

 from its sheath, and separating itself, as seen in the 

 drawing. Little is accurately known of its habits, as it 

 is very scarce. 



390. Vorticella ringens. — The chalice Vorticella is 



* Technical Rep. V, 6. 



