!»i>8 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXVIII. 
tube passes completely to tbe base of the colony, with an opening to the sand 
beneath, situated juore or less centrally among the “ rootlets”. The upper 
end coramimicates with the exterior usually by a simple wide opening, 
occasionally by two. Such apertures occur on the side of the trunk towards 
its summit, well concealed by the bases of the main branches which spring 
from this region. 
When the Spongodes colonies have lain about for some time after collection, 
the ‘ pockets ’ and tubes are found empty ; when examined immediately the 
divers bring them up, a small rounded crab, a Dromia, an inch to an inch and a 
half across the carapace, covered with a velvety coating of short golden brown 
hairs, is found lodging in many — not in all, for this Dromia can be 
activ'c at times wlien danger is apprehended and in the cases where his tube 
has an opening to the sand beneath, he sometimes has time to slip down and 
shake liimself free of the colony as this is being drawn by the diver from its at- 
tachment in the sand. His smooth velvet coat facilitates this escape through the 
lower opening of the burrow. One Dromia only is found in each Spongodes 
colony. Fragments of Spongodes branchlets, bearing polyps and having every 
apjiearance of having been nipped og recently, are frequently present in the 
tuhular burrow, giving rise to the inference that Dromia uses his host’s body 
not only as a dwelling place, but also as a constantly renewed larder ; in such 
case the intruder conics really within the dehnition of parasite rather than 
commensal. Very often the walls of the tubular pocket or tube wherein the 
crab lives, is tinted a distinct red. At hrst I took this for a development of red 
spicules in the walls, due peihaps to special irritation, but closer examination 
proved it to be owing to the presence of more or less broken spicules lying loose 
in a mucous layer on the inner surface of the tube. It is probable then that these 
broken spicules are detritus from the food consumed by the crab. Quite fre- 
quently the scars where branchlets have been nipped og, can be seen on the 
surface of these crab-frequented Spongodes. 
As showing the great frequency of this peculiar association, on one day out of 
twelve Spongodes colonies obtained from the Kallatidal Par (Ceylon Pearl 
Banks) from a depth of 5 to 5^ fathoms, gve contained these symbiotic crabs, 
lodged in tubular cavities excavated in the trunk. In three instances the cavity 
went right through the base and opened among the rootlets. In the other two 
it went far down the trunk, but did not perforate the base. The upper 
aperture of the tube was usually close to the summit of the main axis but to one 
side ; in one case two apertures were present close to the top, while in another 
the opening was only about half way up the trunk. My observations convince 
n»e that these cavities are induced by the O'ab, but whether they are formed 
by the crab forcing its way in by continued and persistent pressure or whether 
they are produced by the tissues of the Spongodes colony gradually growing 
upwards and around the crab, we cannot as yet say. It is a well-known habit 
of many species of Dromia to detach fragments of sponges and compound asci- 
dians from their original attachment, and to hold the fragment over the carapace 
rvith the aid of the specially modihed hinder thoracic legs until such time as the 
fragment has grown and shaped itself on the under side, exactly to the convex- 
ity of the crab’s carapace. How this habit has been niodihed in the case of 
Spongodes has yet to be discovered but I am inclined to think that the associa- 
tion is formed early in the life of both organisms, and that from a small depres- 
sion in which the crab hrst lodged for safety, the subsequent change to a long 
wide tube is due to the continued presence of the crab necessitating the axis 
to grow upwards as a hollow cylinder instead of a Solid one. I do not consider 
it to be a gall-like growth but merely an aperture in the tissues kept open by 
the mechanical presence, not necessarily causing irritation, of the intruding 
crustacean. Possibly however the crab may help mechanically in the forma- 
tion of the burrow by pinching and pulling the tissues. 
