1900.] CuNNiNGTON. — Sea-sJiore Crabs. 125 



perfect little tube placing him in communication with the 

 outside world. The process of burrowing will then go on still 

 further, until nothing remains visible but the tip of this tube. 

 Resting thus passivelj^ in its bed of sand, Corystes spends the 

 daytime concealed from observation, though at night it 

 apparently comes out, and wanders about in search of food. 

 One operation at an}^ rate — that of respiration — has to be 

 carried on even beneath the sand, and this is effected through 

 the medium of the antennae tube. By experiments in which 

 coloured water was introduced close to the tube of a buried 

 crab, it has been ascertained that the water is always sucked 

 down through it, finally passing out from the gill chambers at 

 the sides. Recalling what is the normal direction for the 

 water flow, it will be seen that the condition here is precisely 

 the reverse. Occasionally, and for a moment or two, 

 apparently when the crab wishes to throw out some objec- 

 tionable particle, the current is changed, and becomes 

 normal in direction. The reason for the existence of this 

 reversed current, as the usual condition, in a buried Corystes, 

 is not far to seek. It is simply the outcome of its burrowing 

 habit, and is a beautiful adaptation to altered circumstances, 

 for it is obviously far more satisfactory to draw water from the 

 clear region overhead than to attempt to suck it in at the 

 sides when buried in sand. 



Turning to the hermit crabs themselves, we find a number 

 of remarkable features to be noticed in them. The most 

 familiar ones to us, those which live in old whelk-shells and 

 the like, are perhaps rather more like the lobsters ; but among 

 the group, we find some, which very largely fill any gap there 

 may be between these two main divisions. 



Dromia, a form which has been taken off the southern 

 British coasts, but which is far commoner in the Mediterra- 

 nean, still approximates to the crabs proper, though a good 

 deal of its tail is to be seen in a top view, and the last two 

 pairs of walking legs are almost shifted up on to its back. 

 This creature, too, may do something towards hiding itself by 

 other objects ; one is often found covered by a sponge. 

 Among some foreign allied forms another plan is adopted, 

 where the animal holds tight by its upturned hind legs to a 

 mangrove leaf, or old bivalve shell, which it carries about 

 with it. 



