LAND CRUSTACEANS. 65 



I. Introduction. 



In the economy of a coral island no group of animals is of greater importance, from 

 the biological point of view, than the land Crustaceans. Their numbers, their ubiquity, 

 their activity combine to give them a prominence, which is all the more marked from 

 the absence of so many of the other land animals of continental areas. They are the 

 chief scavengers of the island, play a great part in the destruction or disintegration of fruits, 

 and probably aid in the distribution of seeds. The work done by them in burrowing along 

 the sandy lagoon shore has a possible importance not hitherto noticed'. And it is likely 

 that their omnivorous appetite renders them enemies of many animals, which cannot be 

 specified in the present state of our knowledge : indeed it is highly improbable that the 

 foregoing paragraph exhausts the list of instances in which their behaviour is a factor of 

 importance in the economy of the island I No study of a coral island, in fact, would be 

 complete without an account of this constituent of its fauna. 



For five weeks, in the months of June and July, 1899, I was with Mr Stanley Gardiner 

 in the Atoll of Minikoi. During this time I gave considerable attention to the structure 

 and habits of the land crustaceans of the island. My observations form the bulk of the 

 present paper, but there is included a report on the forms collected by the expedition 

 in the Maldives. In treating of Minikoi I shall begin with a short enumeration of the 

 various species to be found thei-e, and the situations in which they respectively live, and 

 then pass on to some remarks on the structure and habits of the land hermit-crabs 

 (Coenobita), and the habits of the true crabs of the genus Ocypode. The report on the 

 Maldive collection ends the article. 



In the section dealing with the genus Coenobita I have thought well to enter into 

 some detail, and this for two reasons. First, that the peculiar habits of these animals 

 give them an interest of their own, and thus lend an importance to the investigation of 

 their anatomy, and secondly that, in spite of several excellent descriptions of separate 

 systems of organs to be found in the series of elegant and accurate works on the com- 

 parative anatomy of the Decapods which we owe to various French observers, there is 

 still need of an account of the organization of a hermit-crab. In that Coenobita presents 

 the Pagurine type in its most highly developed form (at least as regards many of the 

 organs), it is the most suitable genus for this purpose. In that it contains land animals 

 only, and is not found in Europe or temperate North America, it is less so. I have 

 endeavoured to overcome this difficulty by indicating, in the course of the article, those 

 points in which, to my knowledge, Coenobita differs from the hermit-crabs of the sea 

 (Paguridae). My dissections have been made on fresh and spirit specimens of the Minikoi 

 species'' only, and principally on C. clypeatus and C. perlatus, but, in the few cases where 

 other information has been available, it has been used to check the dissections. Except 

 in a few instances, the musculature has not been dealt with, and histological details have 

 been entirely avoided. 



The introduction to this paper would not be complete without an acknowledgment of 

 the generosity of the Drapers' Company of London and of the Managers of the Balfour 



' See below, p. 95. (1901). 



- See e.g. Alcock, Sci. Mem. Med. Off. Ind., xii, p. 59 ' See below, p. 68. 



G. 9 



