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 iill 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 and are withdrawn closed, previous to being opened and charged 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 Eev. Dr. Lockwood,^ who observed the habits of 

 L. ijohjjjhemiis 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 

 giving 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, i.e. 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." 



' Tr. Linn. Soc. xxviii., 1872, jj. 472. 



