PAGURIDEA THE ROBBER-CRAB 



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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 egg's. The extraordinary 

 asymmetry of these limbs compared with the complete symmetry 

 of the abdomen itself is only explicable on the hypothesis that 



Fig. 119. — Birr/us latro, $ , x J, ventral view. Ab, First pleopod ; T, 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 l^elonging to the last thoracic 



