I 73 ! 
small, but one of the pincers of the first pair is enormous- 
ly developed When alarmed it makes a sharp clicking 
noise with these pincers, so loud that when the little 
creature has been placed into a glass jar of sea water, it gives 
the impression as if the vessel had become cracked.— Conspi- 
cuous everywhere at low tide are the Hermit Crabs {Pagurus 
and other genera), dragging behind them the shells which they 
inhabit. That they are not crabs, but really belong to the 
Lobster tribe, is shown by their long, though soft-skinned and 
twisted abdomen, a condition which has come about through 
their curious habit. No Hermit Crab inhabits the same sheSi 
throughout life, but changes as its growth in size neces- 
sitates a larger house.— Closely allied lo the Hermit Crabs is 
the Robber Crab [Birgus latro), found on the islands of the 
Indo-Pacific seas. Several specimens from Christmas Island 
are exhibited (see pi XVIII, fig. i). These huge beasts are 
abundant on the island, they live and breed on dry land and 
have never been known to enter the sea. They are most in- 
quisitive, obtruding their company where they are not wanted, 
entering even camp and tents at night time. 
MANTiS-SHRIMPS (Stomatopodal 
The Stomatopoda comprise a single family, the SqmlUdae 
or Mantis-Shrimps, so-called because their chief pair of limbs 
resembles the front legs of the Praying Mantis (see p. 6l). These 
limbs fold up like a pocket knife and can inflict serious wounds. 
The body of these animals is much elongated, the abdomen is 
broad and strong and ends in a powerful tail fin. An unusually 
large specimen of a Squilla, measuring I2j^ inches in length, 
obtained at the Fish Market in 1899, is exhibited. There is 
also a beautifully black and white banded species* from Cocos 
Keeling Island, presented by Mr. K. Maclean in 1904. 
BARNACLES (Cirripedia), 
The Barnacles would at the first glance seem to have 
little in common with the Crustacea, their shells reminding of 
the Molluscs. However* their larval stages and their internal 
structure show that they are true Crustaceans. The young 
ones, when first hatched, have three pairs of appendages and 
are free swimming, but after several moults and other changes 
the larvae settle down and develop a shell consisting of several 
pieces. The full-grown barnacles have generally six pairs of 
