72 



L. A. BORRADAILE. 



The fourth and fifth legs (B — E, fig. 17) of each side are markedly smaller than the 



preceding ones. Each of them is chelate 

 after its own fashion, and each bears a 

 part in the work of holding the animal 

 into its shell. This is accomplished by 

 means of a definite patch on the pro- 

 podite of the limb, which is covered with 

 a fine sculpture in the form of rounded 

 scales, overlapping one another so as to 

 produce a surface capable of friction. In 

 cases, which often occur, when the animal, 

 either from its size, or from the lack of 

 suitable gastropod shells, is forced to con- 

 tent itself with some other receptacle for 

 its abdomen', these limbs have to take 

 a larger share of the work in which they 

 ordinarily assist the sixth abdominal ap- 

 pendages, of keeping on the " house." It 

 is probably by their means also that the 

 animal is able to emerge from the shell 

 when it is inverted. The chela of the 

 fourth leg is of a peculiar nature. The 

 propodite, on which the above-mentioned 

 patch is developed, is a broad, discoidal 

 structure. Against this disk fits a little 

 sickle-shaped dactyle. In Fagurus the limb more nearly approaches a normal chela, in 

 Eupagurus it is sub-chelate. The fifth leg has a chela which is clumsy, but of the ordinary 

 shape, with two approximately equal fingers. As in the other forms (Anomala) in which it 

 is a gill-cleaning organ, it is covered with hairs and usually carried under the branchiostegite 

 during life, though upon occasion it can be used to assist in retaining hold of the shell. 



The abdomen is connected by a narrow waist with the thorax. It is covered with a 

 soft, flexible skin, save for a narrow transverse ridge representing the tergite of each of 

 the first five abdominal segments, and broader plates on the sixth segment and telson. 

 The whole is spirally twisted to the right, to fit in with the dextral twist of an ordinary 

 gastropod shell. In correspondence with this twist, the appendages are also asymmetrical. 

 In the male they are absent from the first five segments", but in the female the second, 

 third and fourth are provided, on the left side with long, biramous limbs, covered with hairs 

 and used in the breeding season for carrying the eggs. The sixth pair of abdominal limbs 

 (fig. 18) are present in both sexes, but that of the right side is larger than that of the left. 

 The exopodite is sickle-shaped and longer than the endopodite ; both are provided, on the 

 outer surface, with friction organs like those of the last two thoracic legs, and the function 

 of the whole limb is obviously to anchor the animal into its shell. 



Fig. 17. Legs of hermit-crabs from left side. A. 1st 

 leg (cheliped), Coenobita rugosus; B. 4th leg, Eupagurus bent- 

 hardus ; C. 4th leg, Pagurus deformis ; D. 4th leg, Coenobita 

 clypeatus; E. 5th leg, Coenobita clypeatus. 1. Stridulatiug 

 organ. 2. Male generative opening. 



1 e.g. the shell of the fruit of Calophyllum or of the = C. dyjjeatus has short, uniramous Umbs on the left side 



coconut. See p. 92. in the 2nd, 3rd and 4th abdominal segments of the male. 



