82 BULLETIN OF THE LIVERPOOL MUSEUMS. 
which had been discovered in the Pacific Ocean by Dana, in the course of 
his great voyage under the command of Wilkes. Irrespective of other peculi- 
arities this was distinguished from all other crabs by a remarkable pouch, in 
which the female carries the young, formed by a prolongation of the lateral 
plates of the abdomen.” 
The singular mode of life of these crabs, which was first observed by 
Semper, who studied them alive in the Philippine Islands, is thus described 
by him. For gall-forming crabs “an association,” he says, “ with living 
corals is indispensable, and the influence of the Corals on the Crabs is as 
direct and important as that of the Crabs on the Corals. Hapalocarcinus has 
hitherto been detected only in pieces of branching corals of different 
genera. . . . . On all these corals the crabs produce a peculiar 
excrescence on the tw igs (so to speak) of a branch ; these growths 
grow opposite each other in such a way that the crab settled between them 
is perfectly surrounded, and thus enclosed, in the gall which gradually 
forms. . . A diseased* exerescence is first produced by the young 
crab establishing itself between the two branches, and the twig thus origin- 
ating takes various forms according to the character of the species of coral. 
In the first instance the two leaf-like tw igs are, of course, far 
apart, so that the crab could easily get in and out ; but as it does not do this, 
it is soon so surrounded by the growing together of the twigs that it must 
remain a prisoner. The creature requires a constant and rapid renewal of 
the water in the gall in which it lives for respiration. . . . +, ines 
in all the crabs of this group the current of water for breathing enters the 
body close to the mouth, and passes out again at the hinder margin of the 
branchial [respiratory ] ‘cavity, the stream passing through the gall must 
always flow in one and the same direction. . . . . The two excres- 
cences on the coral grow together quickest in those spots which are least 
exposed to the current through the gall . . . . at length only two © 
fissures . . . are left, which plainly show . . . that it is through 
them that the current for respiration passes. . . . These two slits remain 
open so long as the crab is alive; no living crab is ever found in a closed 
gall, and they are for the most part perfectly empty.” 


* The excrescences show, as stated above, no signs of disease. 


