RESPIRATION^ IN SAND-BURROWING CRABS. 23 
to the ventral aperture through the gap between claws and 
breast. Thus Crabs which conceal themselves just below the 
surface of the sand were enabled to draw their water with 
relative ease from the general reservoir above them. 
In many exotic types, known as Box-crabs from their habit 
of “ shutting-up,” the sides of the shell were smooth and devoid 
of filtering spines, but the same purpose was clearly discharged 
by crest-like expansions, divided into spines and notches on 
the upper edge of the claws themselves. The Mediterranean 
Calappa is an example of this type. 
In other cases in which the Crabs bury themselves deeply 
below the surface of the sand, as in the Masked Crab (Corystes) 
of the English coasts, the claws are not utilised at all for 
respiratory purposes, and are not adapted to the curvature 
of the shell. But the antennne are remarkably long and fringed 
with a double row of curved hairs, which by juxtaposition 
constitute a regular supply pipe reaching to the top of the sand 
in which the Crabs lie buried. By a reversal of the normal 
mode of breathing the Crab sucks its supply of water down 
this antennal tube into what, in other Crabs, is the exhalant 
aperture to the gill-chamber ; while the water, after bathing 
the gills, escapes behind through the aperture which usually 
serves for its entrance. 
The Crab Atelecyclus is remarkable as a connecting link 
between the Portunid type and Corystes. Its antennae are 
short, but constitute together a funnel for the entrance of 
water when the Crab lies buried in the surface layer of sand. 
If disturbed, however, the Crab burrows more deeply into the 
sand to a depth of several inches, where its antennae are useless 
for this purpose. Under these circumstances the Crab is 
entirely hidden from observation, but by sinking a glass tube 
down to various parts of the body in succession, and watching 
the course of coloured water introduced through the tube, it 
was found that the crab folds its Claws beneath the margin 
of the carapace, after the manner of the Portunids, and uses 
also its other pairs of legs, which are provided with dense 
rows of bristles, to enclose a reservoir of water beneath its 
body. This reservoir supplies the gill-chambers with water 
