VI PAGURIDEA—THE ROBBER-CRAB 175 
the much reduced and rudimentary pleopods of that segment, 
and on the left hand side of the body in the female are three 
well-developed pleopods of the first, second, and third segments, 
which are used for carrying the eggs. The extraordinary 
asymmetry of these limbs compared with the complete symmetry 
of the abdomen itself is only explicable on the hypothesis that 
Fie. 119.—Birgus latro, 9, x 4, ventral view. Ab, First pleopod ; 7, last pereiopod. 
these animals are descended from Hermit-crabs which had _ lost 
the pleopods on the right side. 
These appendages are entirely absent in the male. The 
ventral surface of the abdomen is curiously warty and rugose, 
and is very soft and pulpy owing to the immense store of oil 
which it contains. 
If we look at the dorsal surface of the abdomen we find that, 
unlike that of the Hermit-crabs, it is completely protected by a 
number of hard plates (Fig. 120, B). Beneath the carapace can 
be seen a number of small plates belonging to the last thoracic 
