132 THE AMERICAN MONTHLY [Jun 
equally efficient as sieves or filters. The solid particles 
in suspension as they pass back drift into the angle where 
the hinder end of the body bends abruptly down. Here 
they are turned forward into a reverse eddy, forwards, 
under and along the median line of the body, till they 
reach the oral region behind the labrum, where the play 
of the mandibles, like that of Apus, sends them into the 
gullet to be swallowed. If the solids in the water be in 
excess, the accumulation against the labrum is too large 
to be dealt with in this way; and the hinder end of the 
body, armed as itis with two strong spines, is, as it were, 
scraped along the median groove, and turned sharply 
downwards and backwards at the end of the stroke, so 
as to scoop away the clogging mass and expel it from 
the shell. | . 
I may note also that by adding carmine to the water we 
can see that the food passes freely from the gut proper 
into the pyloric caeca, which are, therefore, not merely 
secreting organs. 
They may often be seen feeding in this way when 
resting by the back of the head against a weed or the 
wall of the vessel. A large sensory nerveends here, and 
possibly the end organ may secrete matter viscid enough 
to fix the animal, so long as it does not execute vigorous 
swimming movements. This “dorsal organ” (or rather 
‘nuchal organ’’) is especially well developed in Sida. 
While the general rhythm of the bulk of the limbs of 
crustacea is backwards, their bases and their epipodial 
appendages tend to work in the reverse direction. This 
is especially visible in the last gill of Daphnia, and is 
notably the case with the gills, ete., of the Decapoda, the 
highest group. | 
The Nauplius larva of Cyclops has a so-called “mastica- 
tory hook” at the base of its second pair of appendages, 
which works into the pharynx just in the same way as 
do the mandibles of Apus or Daphnia.—Quwekett Club. 
