NOTES ON THE BEII\VIK ( >F Till-: FIDDI.I-.K < K \B. 



middle corresponding to the space between the plates. If we 

 put a crab into the apparatus it begins to dig and as it can dig 

 only between the plates it may be watched during the whole 

 work. When the crab reached about the half of the height of 

 the sand column I turned the apparatus at right angles. Uca 

 changed then the direction of digging, working now nearly at 

 right angles to the previous direction. Some of such burrows 

 may be seen in Fig. 3. 



FIG. 3. Effect of turning the apparatus at 90 a, b, c, burrow of the same 

 individual. For explanation see the text. 



Clark (4) extirpated both inner antenna of Uca pugilator. 

 He states that the normal equilibrium of the animal was some- 

 what damaged and there was a tendency to roll over. But at 

 the same time the normal conditions, as feeding and burrowing, 

 remained unaltered. Clark has not investigated the shape of 

 the resulting burrows which could possibly furnish some inter- 

 esting conclusions. For the moment we can say only that 

 gravity is one of the factors affecting the shape of the burrow. 



2. Another question connected with burrowing is the question 

 of breathing. The interesting paper of Abbott dealing with the 

 effect of distilled water upon the fiddler crabs (i) contains many 

 important data. The gills of Uca are situated at the bottom of 

 the large gill-chamber and the space over them is tilled with 

 liquid. Abbott thinks that this liquid has only about one-fifth 

 of the concentration of the sea water. The gill-chamber com- 

 municates with the exterior by means of a canal, the opening of 

 which lies between the basal joints of third and fourth legs. In 

 this way the liquid of the chambers may exchange gas with rhe 

 exterior. " In other words the crab when out of the water is 

 able to breathe air" (i, p. 170). The invariable presence of an 



