Hapalocarcinus, the Gall-forming Crab, etc. 41 
branch of which it forms part. A perfect forest of twigs covers the 
surface of galls of some standing and occasionally examples are to be 
observed in which the gall is the foundation of a complex branching 
system. In these cases the galls can evidently lay claim to a respect- 
able antiquity. As long as the crab lives the cavity remains in con- 
nection with the exterior by means of the circle of apertures. Sometimes 
a gall is seen where the crab is dead and all apertures have closed up. 
THE GALLS IN SERIATOPORA HYSTRIX. 
This coral grows only in the sheltered waters of the inner reef, though 
very widely distributed there, and there is little modification of the 
manner of branching. The colony consists of slender cylindrical 
branches of approximately equal diameter, diminishing slowly towards 
Fig. 3.—Gall-formation in Seriatopora hystrix. 
A. Fragment of normal colony, showing dichotomous branching and fusion of adjacent branches. 
B, C, D. Views of a single gall formed at the junction of three branches, 1, 2, 3. 
B. One of its component laminz formed by growths of ccenenchyme from branches 2, 3; the 
outlines of these branches are still preserved; the black spots show the thece of the 
colony regularly arranged on the original branches; not so much so on the new growths. 
C. Side view showing processes from branches 1, 2 fusing together. 
D. Similar view of other side, showing junction of processes from branches 2, 3. 
E. Another gall, showing how each lamina is made up of a number of small branches fused 
together. (From a specimen in the Cambridge University Museum of Zoology.) 
Natural size. 
the sharp apex. It has then a very spiky appearance. ‘The branching 
is regularly dichotomous and where adjacent branches come into con- 
tact they fuse, as is seen in the accompanying figures. Where branch- 
ing takes place at the apex the space between the branchlets is entirely 
inadequate to shelter even so small a creature as the young Hapalo- 
carcinus. For this reason the galls are found not at the surface of the 
colony, as in Pocillopora, but between more basally situated branches 
where a broader lodgement is offered. 
When the crab is established a very marked interference with the 
growth of the coral takes place. The normal growth is greatly stimu- 
lated, a much more considerable addition to the ccenenchyme appearing 
DR 
