Brachionus urceolaris, Melicerta ringens, Stephanoceros eichhorni 

 The figures in tlie background are algae 



disc. Melicerta ringens, as an example of 

 case-builder, possesses a so-called pill-or- 

 gan which is an open sac fringed with ciliae, 

 placed innnediately below the mouth. This 

 sac catches stray little grainlets and turns 

 them into pills with the aid of mucus or 

 slime. These are then carried out and de- 

 posited along the upper edge of the case, the 

 whole case being built up of such "pills." 

 Rotifers can withstand drying up for some 

 time, being then blown about with the dust, 

 and thus carried far and wide. When they 



again reach water they flourish as before. 

 This state of anabiosis (lifelessness) is a 

 well-known phenomenon shown by many 

 organisms which after 200 years of obser- 

 vation still is not well explained. Rotifers 

 can remain in such an inert condition for 

 months and years with impunity. Possibly 

 they exude a jelly-like substance which 

 seals them up and so retains a certain 

 measure of moisture which carries the ani- 

 mals through the period of drowth. 



35 



