PROFESSOR OWEN ON LIMULUS POLYPHEMUS. 191 



whole animal sinks deeper in its bed, till it is hidden all except the eyes. The great 

 over-arching shield of the carapace again prevents one from seeing whether this excavating 

 work is being aided by the fanning motion of the branchial false feet, but I think such a 

 fanning is going on, as I have seen signs of sand being driven out as if urged by a 

 current of water. 



" Mr. Lloyd thus describes the use of the tail-spine in locomotion : — ' The animal 

 having climbed up a rock in the aquarium till it has got near the top of the tank (which 

 in Hamburgh contained a depth of thirty inches of water), and having assumed a vertical 

 position, it leaves go its hold on the rock and allows itself to fall back into the water ; but 

 its downward fall is instantly checked, and the creature propelled upwards by the 

 powerful flapping of its false branchial feet, and when the impetus given by these appen- 

 dages ceases the animal again sinks down, but is prevented from falling prone on the 

 floor of the tank by alighting on the tip of its tail-spine. The moment this happens, 

 and before the creature has lost its balance on the spine, the false feet make another flap 

 and give another impulse upwards and forwards ; all this time the position of the carapace 

 is slanting, the top inclining downwards at an angle of about 45°, the hinder shell being 

 at another angle, and the tail-spine hanging down vertically, and so it progresses by a 

 combination of flapping and hopping till it reaches the limits of its tank and sinks to the 

 ground. The Limulus was fond of thus going about at night, generally remaining on the 

 sand all day. 



" 'Another use made of the tail-spine was as a lever by means of which it righted 

 itself when it fell off a rock on its back. The spine is then bent, 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, and the crab then 

 turns over.' 



" The maxillipeds, no doubt, aid in burrowing, but the chief fossorial agent, as 

 indicated by the size and disposition of the principal muscular masses, is the great 

 ' cephaletral ' digging shield. 



" In an interesting paper by the Rev. S. Lockwood, he thus describes the American 

 species : 



"'The King-Crab delights in moderately deep water, say from two to six fathoms. 

 Except in the case of the very young, which are probably carried hither and thither by 

 the tidal flow, it never seeks the shallow water save for the purpose of reproduction. 



" ' It is emphatically a burrowing animal, living literally in the mud, into which it 

 scoops or gouges its way with great facility by means of the anterior edge of its enormous 

 cephalic shield. In the burrowing operation the forward edge of the anterior shield 

 is pressed downwards and shoved forwards, the two shields being inflected, and the sharp 

 point of the tail presenting the fulcrum as it pierces the mud, while 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 excavating action, for the alternate doubling up or 



