Hapalocarcinus, the Gall-forming Crab, etc. 63 



a spherical colony of Leptastrcea solida, about 4 cm. in diameter, 

 from Minikoi, 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 tennis (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 chelae 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. 



