1 84 J AN IJ - DEMBOWSKI. 



Besides photo- and thigmotaxis there is a strong hydrotaxis, 

 the crab striving towards the moisture. There exists also a very 

 marked tendency of hiding itself in the sand. Especially in 

 females we may see often a behavior distinctly different from the 

 ordinary burrowing. It consists in a quick pressing of the body 

 in the sand. As the friction is very strong the animal succeeds 

 only in hiding the thorax while the legs of one side of the body 

 remain uncovered. In this position the crab may remain motion- 

 less for hours and such a behavior certainly has some biological 

 significance as very little is seen of the crab, the legs having a 

 marked protective coloration. The consistency of the ground 

 has also some influence on the choice of the spot where the 

 work is started. If we make a shallow hole in the sand Uca will 

 choose it as the starting point. All those "taxies" and strivings, 

 and many more, determine the actual behavior and referring 

 the activities of a crab to some particular tropism is rather a 

 poor explanation. 



However, at last the animal starts its work. To simplify the 

 nomenclature I shall use roman numbers I.-Y. for the legs of 

 the side of the large claw of the male, and the arabic 1-5 for the 

 legs of the opposite side. Thus I. means the large chela, i 

 the small one. 



At the very beginning of the work the side 1-5 is usually 

 directed towards the wall of the jar, straightly or obliquely, and 

 usually this side begins to dig. The legs 2, 3 and 4 which are 



FIG. 2. The second leg from the side, st, sternum ; < . ri>x<>pi>dit ; '' basipodit ; 

 i. ischiopodit; m, moropodit; ca. carpopodit; />, propndit; d, dactylopodit. 

 There is no movable articulation between h and /. Articulations p-d, m-ca and 

 c-b work in the same plane, others at right angles to tin-in. 



bent in the articulations mero-carpopodit and dactylo-propodit 

 at the normal position of the body become somewhat stiff. At 

 the next moment they become bent a little more in both articu- 



