64 MARVELS OF POND-LIFE. 



motions, and one, or perhaps two, spiral threads 

 extend through the upper half of its length, and 

 either act as muscles, or as elastic springs for its 

 extension. The intestines and other viscera are 

 clearly exhibited, and a strong ciliary action con- 

 ducts the food to the gizzard-mouth. 



To return to the tail. One spiral fibre is easily 

 discovered; but I have often, and at an interval 

 of months, seen the appearance of two, and am in 

 some doubt whether this was a deception, arising 

 from the compression employed, or was a genuine 

 indication. 



TThere this Rotifer occurs I have usually found 

 it plentiful, but unfortunately could obtain no con- 

 stant supplies after T had determined to make a 

 special study of the remarkable tail, wliich is 

 much more complicated than I have described. 

 The Ptero'lina lived for some time in captivity, 

 and for a week or two I could obtain them fi'om 

 my glass tank. They were likewise to be found 

 for some weeks in the same part of the pond, 

 but not all over it, until one day not a single 

 specimen could be discovered, notwithstanding a 

 persevering search, nor was I afterwards able to get 

 any from that pond during the remainder of the 

 year. 



Several other Rotifers, with and without carapaces, 

 were among the same mass of conferva, among them 



