THE FILTERING APPARATUS. 59 
floor of the pyloric chamber were flat, a wide triangular 
passage would thus be left open in its lower half. But, 
in fact, the floor rises into a ridge in the middle, while, at 
the sides, it adapts itself to the shape of the two cushion- 
~shaped surfaces; the result of which is that the whole 
cavity of the posterior part of the pyloric division of the 
stomach is reduced to a narrow three-rayed fissure. In 
transverse section, the vertical ray of this fissure is 
straight, while the two lateral ones are concave upwards 
(fig. 9, #). The cushions of the side walls are covered 
with short close-set hairs. The corresponding surfaces 
of the floor are raised into longitudinal parallel ridges, 
the edge of each of which is fringed with very fine hairs. 
As everything which passes from the cardiac sac to the 
intestine must traverse this singular apparatus, only the 
most finely divided solid matters can escape stoppage, so 
long as its walls are kept together. 
Finally, at the opening of the pyloric sac into the 
intestine, the chitinous investment terminates in five 
symmetrically arranged processes, the disposition of 
which is such that they must play the part of valves 
in preventing any sudden return of the contents of the 
intestine to the stomach, while they readily allow of a 
passage the other way. One of these valvular processes 
is placed in the middle line above (figs. 10 and 11, v4). 
It is longer than the others and concave below. The 
lateral processes (v?,) of which there are two on each side, 
are triangular and flat. 
