The Masked Crab 205 
sand, it spends its days buried 
beneath them, coming out at 
night into the open waters to 
feed. Its trunk 1s narrowed 
in order that it may sink 
rapidly into the sand, the 
posterior portion being re- 
duced in thickness with the 
same object. The extreme 
jomts of the eight smaller 
limbs are made hard and 
pick-hke that they may 
begin the excavation; then 
they are curved to get a 
hold whilst the long nipper- 
arms are pushing the trunk 
backwards and downwards. 
Thus it will be seen that Z 
everything is adapted for a MALE. 
rapid disappearance of the 
crab, for the sandy flats are much frequented by 
destroy it. 
The underside of the trunk is clothed with 
FEMALE. 
fishes that would otherwise soon 
fine hairs, and the smaller limbs 
are fringed so that when drawn up to the body they prevent the fine sand from 
passing under the upper crust and injuring the delicate breathing apparatus. In order 
to ensure a constant supply of oxygenated water for the gills, the feelers or antenne 
have been developed to a great length, stiffened, furnished with a double frmge of 
long hairs, and their basal joints so modified that they may be held out straight in 
front, when the hairs interlock and form a skeleton tube through which water may 
pass, whilst the grains of sand are kept back. Thus equipped the Masked Crab can 
lie snug and safe beneath the sand, whilst the antennal tube keeps open communication 
with the water above, and the tips being exposed 
part of her food 
so-called “ tail.” 
allow sensations of what is happening in the world 
of waters to be conveyed to the crab’s brain. 
So far what we have described is more particu- 
larly the outward signs of the male crab. The female 
may be readily distinguished by the fact that her 
nipper limbs are little more than half the length of 
these organs in the male. Why should this be so? 
Well, the female is not nearly so active as her 
mate, and those who have kept her alive in aquaria 
know that she will remain buried for weeks con- 
secutively. It is probable that she finds the greater 
among the sand surrounding her, 
so the long lever-like arms are not so necessary in 
her case. Another modification will be found in the 
In all the typical species of crabs 
the last seven jomts of the trunk are verv thin and 
bent under the body. In the males these “tails” 
are of very slender proportions, but in the females 
~- : — = = Pp . . a . 
UPPER SIDE 0 MASKED CRaB. they are very broad, forming a kind of pouch in 
