A STUDY OF A CRUSTACEAN. 55 



Tellina and Hydrobia, abundant lower down the estuary, were 

 here very scarce ; and the only worm was Nereis dumerilii, which 

 existed in very scanty numbers in burrows half a yard deep, and 

 was apparently absent from large parts of the ground. Areni- 

 cola, although abundant in Morecambe Bay, and at the mouth 

 of the estuary, did not occur on the area I examined at Sandside. 



The dominant animal was the Amphipod crustacean, Coro- 

 phium longicorne ; so far as I know, there was no part of the 

 shore free from this organism. It burrows in the sandy mud, 

 making U-shaped passages about two inches in depth, and 

 throwing small castings on the surface. In an aquarium these 

 castings take the form of fairly stable tubes projecting for half 

 an inch or so above the sand, but in the moving waters out of 

 doors, or on the exposed surfaces, the material is merely piled up 

 at the mouth of the burrow. The castings indicate the presence 

 of the animals ; and, as I have said, this square mile of sand 

 was dotted with them. Their number varied, but I did not take 

 the trouble to count the castings ; I did, however, make many 

 counts of the numbers of crustaceans present in different square 

 inches of sand, never seeing less than fourteen, nor more than 

 thirty-five. Near Humphrey Head, on the Lancashire coast, the 

 animal is unevenly distributed, being absent from the pure sand, 

 and abundant in the muddier gutters ; and in these I found that 

 a single square inch of sand contained over fifty crustaceans in 

 various stages of development. In September Mr. A. Kodgers, 

 examining the shore at Silverdale for me, found them quite 

 absent from the great stretches of the comparatively pure sand. 



For the present investigation round numbers will be quite 

 sufficient, and we can take twenty as the number of crustaceans 

 inhabiting each square inch of the shore at Sandside. Eleven 

 animals of various sizes picked at random and drained on 

 blotting-paper weighed altogether exactly two grains, and this 

 gives us a total of over seven hundred tons of these crustaceans 

 for the square mile. The preponderance of Corophium over all 

 other forms of visible invertebrate life enables us to dismiss the 

 molluscs and worms, and the resulting simplicity allows us to 

 consider the subject from an interesting point of view. 



The burrows I examined never reached a greater depth than 

 two inches, and most of them were little more than an inch. I 



