88 A HISTORY OF RECENT CRUSTACEA 
persons who might be familiar with the smooth flat sur- 
faces opposed to one another in the legs of a crab, and 
who yet would never make the guess that it was an 
arrangement to diminish friction. With the guess made 
for them by some one else they would be contented for 
another lifetime, and so on perhaps with the objection to 
the guess that if friction was to be avoided, the legs would 
not have been fringed with hairs. Fritz Miiller was well 
aware of the old principle that Nature makes nothing in 
vain, and was pretty confident to begin with that there 
would not at the same point be two arrangements counter- 
acting one another, the one increasing and the other 
diminishing friction. The smooth surfaces of the lmbs 
enable them to act as tight-closing lips to the breatking- 
aperture which he discovered at their bases. As to the 
fringing hairs Fritz Miiller hazards the conjecture that 
they may be olfactory. This might seem a very extra- 
vagant supposition, that a crab should have the equiva- 
lent of a nose attached to its legs, did we not remember 
that some crustaceans have organs of hearing in the appen- 
dages of the tail. Moreover, Fritz Miiller observed that 
in his Ocypode the olfactory filaments in their usual place 
on the antennee were much reduced, and that the flagella 
of the antennz never make the peculiar beating move- 
ments familiar in other crabs, and he argues that in an 
air-breathing crab, just as in the air-breathing vertebrates, 
the sense of smell might be expected to have its organ at 
the entrance of the breathing cavity. 
Gelasimus, Latreille, 1818, meaning the laughable crab, 
is a genus containing a large number of species that haunt 
warm climates. Here, too, the orbits and eye-stalks are 
long. The pleon in the male is narrow and distinctly 
seven-jointed, and its base does not occupy the whole 
width of the sternum between the walking legs. But the 
most striking feature is the disproportionate size which in 
the male is attained by either the right or the left 
cheliped. 
According to de Haan his species Gelasimus arcuatus 
is called in Japanese Siho maneki, which means ‘ beckon- 
