148 SYDNEY J. HICKSON, M.A., F.R.S. 



On the specimen in the Derby Museum, Liverpool (Fig., p. 80), 



there are three galls, two complete and one in process of formation. 



Of the three galls the lowermost (a) in the figure is the oldest. It 



is about 30 mm. long by 25 mm. broad, and the aperture is oval, 



8 mm. by 6 mm. in size. 



The cavity is large, its diameter being considerably greater than the 

 greatest diameter of the aperture. The dried crab remains in this gall, 

 but as it would be impossible to extract it without injury, I am unable 

 to say more about it than that it is very much smaller than the cavity 

 in which it lives. 



The second gall (b) is smaller and much more spherical in shape, its 

 diameters being approximately 20 mm. The aperture is relatively 

 larger than that of the other, being 6 mm. by 7 mm. in size. It 

 contains no crab. 



The imperfect gall at the top (c) is widely open, and is formed of a 

 network of Millepore branches imperfectly woven together. 



The extent of the malformation produced by these crabs need not be 

 described as it is adequately represented in the illustration, but, I may 

 add, the surface of the coral forming the outer wall of the gall shows 

 no signs of unhealthiness or weakness. The cycles of pores are as 

 numerous and as regular as in other parts of the corallum with normal 

 growth, and the pores themselves are just as large and as well defined 

 there as elsewhere. 



These galls cannot, therefore, be regarded as a disease, although they 

 effect a considerable alteration in the normal groAvth of the corallum. 



Note. — The description of the gall-forming crab, given by Dr. 

 Semper, and referred to above, is as follows : — " So long ago as the 

 year 1837 Stimpson described a small crab, under the name of Hapa- 

 locarcinus marsupialis, 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 peculiarities 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 indispensible, and the influence of the Corals on 

 the Crabs is as direct and important as that of the Crabs on the Corals. 



