42 Papers from the Department of Marine Biology. 
than would be made in the normal thickening of the branches. Thin 
laminar expansions grow out from the sides of the branches in a plane 
parallel to that of the crab’s respiratory current. These lamine do not, 
however, represent continuous growth, but are formed by the coales- 
cence of parallel twigs which can be easily distinguished at the edge 
of lamina. This is perhaps best illustrated by a specimen in the Cam- 
bridge University Museum of Zoology, which is shown in figure 32. 
The numerous gaps which occur in the walls of the gall are due to the 
incomplete fusion of the component twigs. 
Fic. 4.—Surface view of colony of Pocillopora cespitosa. 
A outside and B inside a gall. X20. After prolonged decalcification, preparations stained with 
borax-carmine. 
In A the polyps are regularly developed, the tentacles and mesenteries are formed of thick, deeply 
staining tissue and the septa are of normal number and symmetrically arranged. 
In B the polyps are stunted and irregular, the mesenteries and tentacles not well developed and 
the septa often placed asymmetrically and sometimes short of the typical number. 
co., coenenchyme, ; oe., cesophagus; mes., darkly staining tissue, mesenteries and tentacles 
indistinguishable; sep., septa. 
The initial result of the interaction of the crab and the coral is the 
production of a small initial chamber as in Pocillopora. Afterwards 
an upper chamber is formed, large enough to contain the mature 
female. The complete gall is not quite so regular as that in Pocillopora, 
but it has essentially the same structure. 
At first sight the interference with the normal habit of branching 
involved in gall formation seems to be much greater in Seriatopora 
than in Pocillopora. In the latter case there is an apparent broadening 
of existing branches, a stimulation of lateral growth as compared with 
apical growth. In the former, however, there is at the point of settle- 
ment a production of numbers of tiny lateral branches which, together 
with the main branches from which they spring, form the walls of the 
gall—a basketwork the meshes of which are filled in by subsequent 
growth. The course of the main branches can always be traced, even 
