62 



Papers from the Department of Marine Biology. 



coral grew more rapidly than the crab, an inverted funnel or hollow cone 

 would be formed over the crab, while, if the crab grew the faster, the margin of 

 its cave-dwelling, so long as it was small, could not be exactly on a level with 

 the margin of the contiguous polyp-cups. But when the crab has reached its 

 full length, about seven millimetres, the polyps outgrow its funnel-shaped 

 dwelling, and would no doubt soon wholly outgrow it, if it were not that they 

 find a certain resistance in the current set up by the crab for breathing and in 

 the movements of the creature; and this resistance is sufficient to compel the 

 growth of the coral in a particular and determined direction. The two powers 

 in opposition thus reach an equilibrium, and it is their reciprocal action which 

 gives the funnel its characteristic form. 



"Here too, as in the former instance [Hapalocarcinus], the individual 

 polyps plainly show the effects of the current. While in general the cups are 

 perpendicular to the surface of the coral, in most of those which grow within 

 the funnel this is not the case; they have an oblique direction upwards, and 

 are most oblique where the strength of the current is greatest, i. e., at the 

 narrow bottom part of the funnel." 



The material I have investigated comes from Minikoi and has 

 already been reported upon by Borradaile (Fauna and Geography of 

 the Maldives and Laccadive Archipelago, vol. i, p. 271, Marine Crus- 

 taceans, III, XanthidaB and some other crabs) and referred to the 

 species Cryptochirus coralliodytes Heller. They were collected by Pro- 

 fessor J. Stanley Gardiner and are preserved in the Cambridge Univer- 

 sity Museum of Zoology. There were three males and several females. 

 The dimensions (in millimetres) were as follows: 



These measurements are very similar to those given by Heller for 

 C. coralliodytes from the Red Sea. 

 The notes given by Professor Gardiner are as follows: 



"A block of Leptoria tennis, which had a large number of round holes on the 

 surface up to 4 mm. across, was broken up. The holes . . . were nearly 

 all found to be occupied by a symbiotic crab. The holes varied in depth 

 from 1 to 30 mm., the coral being in the latter case 48 mm. thick. Nor- 

 mally the animal would appear to live close to the surface, with the carapace 

 as a kind of shield closing the hole. When the block becomes more or less 

 dry they retreat into the bottom of the holes. . . . These commensals 

 are extremely common in Leptoria from the lagoon at Minikoi, but are never 

 found in specimens from the outer reef. They are rare on other corals, occa- 

 sionally in massive Astrseids from the lagoon at Minikoi, but not apparently 

 in branching corals, fungoids, or perforate corals." 



I examined a number of colonies in a dried condition from the col- 

 lections of Professor Stanley Gardiner and Mr. Cyril Crossland. In 



