rotifer: Numbers of Rotifers by Fluid Density
Description
The data give the numbers of rotifers falling out of suspension for
  different fluid densities. There are two species, pm
  Polyartha major and kc, Keratella cochlearis and
  for each species the number falling out and the total number are
  given.source
D. Collett (1991) Modelling Binary Data. Chapman & Hall. p. 217