. Animal life as affected by the natural conditions of existence. Animal ecology. GALLS ON CORALS. 217 carcinus marsupialis, which had been discovered in the Pacific Ocean by Dana, in the course of his great voyage under the command of Wilkes. Irrespective of other peculiarities, this was distinguished from all other crabs by a remarkable pouch in which the female carries the young, formed by a prolonga- tion of the lateral plates of the abdomen. Subsequently Heller described another species of crab from the Red Sea, under the name of Cryptochirus corallioclytes, of which the female has egg-po
. Animal life as affected by the natural conditions of existence. Animal ecology. GALLS ON CORALS. 217 carcinus marsupialis, which had been discovered in the Pacific Ocean by Dana, in the course of his great voyage under the command of Wilkes. Irrespective of other peculiarities, this was distinguished from all other crabs by a remarkable pouch in which the female carries the young, formed by a prolonga- tion of the lateral plates of the abdomen. Subsequently Heller described another species of crab from the Red Sea, under the name of Cryptochirus corallioclytes, of which the female has egg-pouches similar to those of the other genus, but the form of the body is otherwise quite different. While the general form of Hapalocarcinus is lenticular, Cryptochirus has a thorax of perfectly cylindrical shape, with a head terminating obliquely, so that it strikingly resembles several of the cylindrical wood- boring beetles. The singular mode of life of these crabs was, however, unknown to both these Fig. 64.—The crabs forming galls on corals, a, Cryptochirus (male) ; b, Corallioclytes (female) ; c, Hapalccarcinus marsvpialis (female). As 1 was able to study both species alive in the Philippine Islands, I will here give my observations in detail. For both of them an association with living Corals is indis- pensable, and the influence of the Corals on the Crabs is as direct and important as that of the Crabs on the Corals. Hapalo- carcinus 102 has hitherto been detected only in pieces of branch- ing coral; I have found it on Sideropora digitata and palmata, and on species of Seriatopora; Verrill found it on Pocillopora ccespitosa in the Sandwich Islands, and D. Graeffe discovered it on two species of Seriatopora. On all these corals the crabs produce a peculiar excrescence on the twigs (so to speak) of a branch ; these growths, which are sometimes very broad and "massive, and sometimes very slender, grow opposite each other in such a way that the crab settl
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