214 MICROSCOPY FOR BEGINNERS. 



Melicerta turns herself in the tube, bends her body, and 

 deposits the pellet on the top row, where she cements it 

 in place with an invisible insoluble cement. The whole 

 is done so quickly that the first time the observer sees 

 it he is so surprised that he sees nothing. It is remark- 

 able that, as a rule, she forms the pellet while standing 

 on the side of the sheath opposite to the point where 

 she means to place it. The pellets have often been de- 

 scribed as round balls, but the student will see that they 

 are conical, and that the pointed ends are on the out- 

 side. Melicerta is quite common on Ceratophyllum. 



6. LIMNIAS (Fig. 146). 



The sheath that this Rotifer forms is a rather stiff, 

 membranous, nearly cylindrical tube, somewhat widest 

 at the upper part. When young it is usually colorless 

 and smooth, but it changes with age, becom- 

 ing brown or blackish, and floating particles 

 roughen it by adhering to the outside. The 

 animal living within it is colorless, and has the 

 ciliary disk divided into two lobes, which she 

 folds together when frightened and forced to 

 retire to the back part of the sheath for pro- 

 tect i n - The sheath is secreted from the body 

 of the Rotifer ; it is not built of particles 

 picked out of the currents from the ciliary disks. It is 

 common on the leaflets of Ceratophyllum, and is prob- 

 ably named Limnias cemtopliylli for that reason, al- 

 though it is found almost as often on Myriophyllum. 



