208 R. Bigalke 



the basal and other segments of the third maxillipedes. Since how- 

 ever the sand is passed forwards between the third and second 

 maxilHpedes it must be the latter which perform the straining pro- 

 cess discussed below. 



Interpretation of the Process. 



The structure of these hairs together with the fact that wet sand 

 is continually being passed forwards as long as the animal remains 

 undisturbed, suggests that they act as a straining apparatus in which 

 either, 



( 1 ) water is separated from the sand and passed backwards 

 over the gills to be used for respiration, or 



(2) food particles are strained off from the sand and passed 

 into the mouth. This seems to be the more probable of the two 

 explanations. 



The process described must therefore be interpreted either 



( 1 ) as being a means of respiration, or 



(2) as being a means of obtaining food. 



Evidence against its being a mode of respiration is afforded by 

 the following facts: — 



(a) Gills are found to be present at the sides of the body under 

 the branchiostegites. Now many species of crabs which breathe 

 normally by gills are known to be able to live out of the sea water 

 for considerable periods, and it seems but natural to infer that this 

 particular species is able to do likewise during the periods of low 

 water. 



(b) When the tide comes in the burrows become closed up with 

 sand, and as far as could be observed the little creatures remain in 

 them until the water again goes out. Hence the only period dur- 

 ing which they are able to take nourishment is during the period of 

 low water, and unless the animals feed during this period it is not 

 clear when they do so. Evidence in favour of its being a method 

 of obtaining food is afforded thus:= 



(a) The process takes place in the region of the mouth. 



(b) A similar method of obtaining food is knovm in other 

 tropical species of sand-burrowing crabs belonging to the 



