x HABITS 265 
of the shell; and in the act of thrusting, the lobes or plates on 
each leg encounter the sand, the resistance or pressure of which 
causes them to open and fill with sand, a load of which at every 
thrusting operation is pushed away from under the king-crab, 
and deposited outside the carapace. The four plates then close 
and are withdrawn closed, previous to being opened and charged 
with another load of sand; and at the deposit of every load 
the whole animal sinks deeper into its bed, till it is hidden all 
except the eyes.” There seems little doubt that the action of 
these appendages in removing the sand from under the carapace 
is reinforced by the fanning action of the respiratory appendages, 
which set up a current that helps to wash the particles away. 
But the posterior walking legs are not the only organs used in 
burrowing. The Rey. Dr. Lockwood,' who observed the habits of 
L. polyphemus off the New Jersey coast, says, “The king-crab 
delights in moderately deep water, say from two to six fathoms. 
It is emphatically a burrowing animal, living literally in the 
mud, into which it scoops or gouges its way with great facility. 
In the burrowing operation the forward edge of the anterior 
shield is pressed downward and shoved forward, the two shields 
being inflected, and the sharp point of the tail presenting the 
fulcrum as it pierces the mud, whilst underneath the feet are 
incessantly active scratching up and pushing out the earth on 
both sides. There is a singular economy of force in this ex- 
cavating action ; for the doubling up or inflecting and straighten- 
ing out of the two carapaces, with the pushing purchase exerted 
by the tail, accomplish both digging and subterranean progression.” 
At night-time Limulus is apt to leave the sand and progress 
by a series of short swimming hops, the respiratory appendages 
ceiving the necessary impetus, whilst between each two short flights 
the animal balances itself for a moment on the tip of its tail. 
During this method of progressing the carapace is slanting, 
forming an angle of about 45° with the ground. The unseg- 
mented tail is also used when a King-crab falls on its back. 
“The spine is then bent, 7. its point is planted in the sand so 
that it makes an acute angle with the carapace, which is then so 
far raised that some of the feet are enabled to grasp a projecting 
surface, either longitudinal or vertical, or at some combination of 
the two; and the crab then turns over.” 
D Tr, Conn. Soc. xxvii. 1872, p. 472. 
