LAND CRUSTACEANS. 



69 



2. Some points in the structure and habits of the land hermit-crabs (CoenoMta). 

 i. External features. 



The genus Goenobita contains those hermit-crabs which have left the sea and taken 

 to a life on land, but have not, like Birgiis, lost the habit of shielding the abdomen with 

 a shell, or some such covering. In their outer, as in their inner organisation, the members 

 of the genus closely I'esemble the hermit-crabs of the sea, and even present many 



Fig. 13. Coeiiobita cli/peatus usiug a broken coconut as shell. 



characteristic features of Pagurine' structure in a more highly developed form than any other 

 branch of the group. The most striking of these features are, of course, those connected 

 with the habit of sheltering within the empty shell of a gastropod mollusk, and it is perhaps 

 worth while recapitulating them, even at the risk of ploughing the sands of well-known fact. 



Physiologically, then, the body may be divided into three regions as regards its outward 

 aspect: (1) a. fore-part carrying the complex of organs — sensory structures, legs and jaws — 

 by which the animal enters into relation with the outer world, and containing internally 

 the central nervous system and stomach, both intimately connected with the external organs 

 just mentioned, and the excretory organs. This part of the body can be completely ex- 

 truded fi-om the shell, while the animal still retains a firm hold on the latter. (2) A mid- 

 part, which, when the fore-part is thrust out, fills the mouth of the shell, and is provided 

 with limbs, which help in retaining a grasp of it. This region carries the main respiratory 

 apparatus — delicate organs which need a certain amount of protection and yet should be 

 in free communication with the surrounding medium— and the heart. (3) A hind-part — 

 the abdomen — which contains the bulky liver and the generative organs, and carries on its 

 appendages the eggs, which thus obtain the shelter provided by the shell. This division 

 of the body, which is at all times completely protected by the shell, is also provided with 

 an apparatus by means of which, in normal circumstances, the latter is retained. This 

 apparatus consists of an anchor, formed by the sixth abdominal segment and its appendages 

 (fig. 18), and a broad band of muscle — the cable of the anchor — along the ventral side of the 

 abdomen, serving roughly the same purpose as the columella muscle of the original maker of 

 the shell. 



' In the present article, the term "Pagurine" will be used 

 to include the most typical members of the Pagurinea — the 



Paguridae and the Coenobitidae. The word " Pagurid " will 

 be applied to the former of the two families alone. 



