Hapalocarcinus, the Gall-forming Crab, ete. 63 
a spherical colony of Leptastrea solida, about 4 cm. in diameter, 
from Muinikoi, there were six pits occupied by dried Cryptochirus 
and a large number of others which resembled the first exactly and so 
were probably once occupied by crabs. Each pit is cylindrical and 
uniform in diameter. At the bottom are to be seen the septa and 
columella of a dead polyp; the walls are perfectly smooth. The depth 
only varies from 4.5 to 5 mm. and in all cases the inhabitants were 
barely mature females. It seems, then, that all these symbiotic crabs 
had established themselves simultaneously or practically so, no very 
long time ago. 
In a fragment of a colony of Leptoria tenuis (plate 3) also from 
Minikoi, and so possibly the very specimen alluded to in Professor 
Gardiner’s account, there were three deep pits measuring respectively 
12,16, and 40 millimetres with a regularly circular cross-section. In the 
first of these was a female Cryptochirus with well-developed abdomen 
(but not bearing developing eggs) much larger than those found in 
the colony described above. There was also a shallow pit only 3 mm. 
deep which contained a male. This observation is of great interest. 
In Hapalocarcinus it is fairly certain that the male never forms galls, 
but leads a short and wandering life. In Cryptochirus dimorphus, 
where the male is very much smaller than the female, a pair is found 
in each pit according to Henderson (4), the male nearly always adherent 
to the female. In this species, then, it may be assumed with certainty 
that the female is the original householder and that the male is a mere 
lodger benefiting by the hospitality of the other sex. But in Crypto- 
chirus coralliodytes, where the disparity in size is not so great, as far as 
my limited experience goes, solitary females usually inhabit the pits, 
but sometimes the males form and tenant very shallow ones, so that 
separate establishments for the sexes is the rule. But the shallowness 
of the pits containing males shows that they are short-lived or given to 
changing their residence. The structure of the males, moreover, is 
not so much adapted for life in a deep pit as is that of the females. 
The walking legs of the second pair are not stronger than the others 
and the swollen chelz are not fitted to assist in scrambling up and down 
a smooth-walled hole. It is obvious that both sexes must leave their 
holes at certain times. The female fits so tightly in her hole that she 
must come to the surface of the coral colony to moult, and so there 
copulation also will occur. 
It seems, then, from the information we at present possess, that the 
three species described in the family present an interesting gradation 
in sexual habit. In Hapalocarcinus marsupialis the male wanders 
about from gall to gall and is very short-lived; in Cryptochirus dimor- 
phus he lives a sedentary existence, but merely as a commensal of the 
female crab; while in C. coralliodytes he actually forms a house of his 
own, where he maintains an independent position. 
