LIITNEAN SOCIETY OF LONDON. 1 9 



there would be a great chance of the animal falling to one side^ 

 that is, it would have difficulty in keeping its balance. But the 

 difficulty is got over in a very simple manner in this particular 

 creature by the use of the chelae as a supplementary means of 

 locomotion. The form {Etipagicrus) is one of which the commonest 

 example, the Hermit Crab {E. bernhardiis), is to be met with all 

 round our coasts, and it is generally found sheltering its soft body 

 in a dead whelk-shell. In the case of this crustacean we have a 

 creature which, so far as I have seen, always crawls in such a 

 fashion that the mouth of the shell which it inhabits faces directly 

 forwards, the lip of the shell immediately overhanging and entirely 

 concealing the carapace, only the sense-organs being allowed ta 

 protrude just beyond the margin of the lip together with the 

 chela^ and two succeeding pairs of limbs. The third and fourth 

 pairs are here greatly reduced in size, and are always kept within 

 the whelk-shell, whose inner surface they are pressed against, 

 serving to assist the abdomen of the Hermit Crab in maintaining 

 its position in the shell. The antennae are usually carried, one 

 pointing in the direction of motion, and the other away from it. 

 "When in motion, the chelae supplement the four other walking- 

 legs, so that the locomotion is of the lateral hexapod type, dif- 

 fering from Inaclius only by the chelae taking the place of one of 

 the pairs of limbs no longer used for progression. 



If this Hermit Crab be moving in the direction from right 

 to left, we may find the following state of affairs : — The right 

 large chela in contact with the ground, with which it has been 

 brought in contact as much to the left as possible, acting chiefly 

 as a support to the body and as a sort of fulcrum upon which 

 the body will move to the left, rather than as an active agent 

 propelling it in a given direction — an exceedingly powerful loco- 

 motive engine. The other limb in action on this, the right side, 

 will be the third counting from the chela, the second being 

 raised. On the left side there will be only one limb in action, 

 viz. the next following the small chela. In the last phase of 

 locomotion there will be two limbs pulling on the left and one 

 pushing on the right. 



A crab in which I believe similar features would be met 

 with is one which, unfortunately, is very rarely found on 

 this coast, although specimens are occasionally taken, and one 

 presenting some exceptionally curious features was some time 

 since obtained somewhere on the Cornish coast near Penzance, 

 as I am informed by my friend Mr. Tregellis. It is a little 

 crab which is known as Dromia. It is a slow-moving species, 

 with short limbs, and the two hind pairs of limbs are always 

 carried bent up over the back, where they are employed to 

 hold on either some pieces of a compound ascidian or a piece 

 of sponge, which are used mainly for concealment, by obscuring 

 the outlme of the body of the crab, but in part also to 

 scare away animals that would otherwise prey upon it. Both 

 sponges and compound ascidians are extremely distasteful to most 



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