122 PEARSE. 



FEEDING AND FOOD. 



Female fiddler-crabs feed by scooping up mud with the hairy, 

 spoon-like fingers of the chelipeds and carrying it to the mouth; 

 the two hands alternate rapidly in this action. The males, how- 

 ever, use only the small cheliped when feeding. These append- 

 ages are well suited for the work they have to do, for their 

 fingers are flattened and hollowed in such a way that admirable 

 dredges are formed for carrying mud to the mouth. Feeding 

 is not attempted when the flats are dry, and it is most active 

 just after the tide has gone out, or along the edge of an advanc- 

 ing tide. The mouth-parts sort over the mud that is brought 

 -to them and a mass of rejected material collects below them. 

 This material slowly drips as the animal moves about feeding, 

 and is frequently wiped away with a cheliped. 



On July 4, 20 stomachs of Uca rathbunse were collected between 

 8.55 and 9.20 in the morning. These were placed at once in 

 10 per cent formalin, and two days later the contents of 6 were 

 examined microscopically with considerable care. The objects 

 discovered were as follows, in the order of decreasing quantity : 

 Plant tissue, a branched alga, vascular plant tissue, small green 

 algse, small bro^vn spores or cysts ( ?) , fine silt, diatoms, protozoa, 

 and a piece of leaf epidermis. Striated muscle fibers were also 

 found in 2 stomachs, but these may have been loosened from 

 the stomach wall of the crab itself. Whether this was true or 

 not, the examination showed that the food of fiddlers consists 

 mostly of vegetable matter. The stomachs of 2 indiviSuals were 

 completely filled A^ith a species of alga and a little fine silt. 

 Probably a portion of the unidentifiable plant tissue consisted 

 of the same alga, which appears to be an important element in 

 the fiddlers' fare. Although these animals seem to take mud 

 from almost any locality, they are not indiscriminate feeders, 

 the chelipeds and mouth parts apparently exercising consider- 

 able care in the selection of food. 



BEHAVIOR. 



A fiddler-crab lives on the mud flats crowded among vast 

 numbers of his fellows, but his intercourse with them shows 

 no development of "social" instincts. He has selected his most 

 suitable habitat, and the fact that he is surrounded by hundreds 

 or thousands of his own kind is more or less incidental. Each 

 fiddler searches the mud around his hole for food and his "hand 

 is against every man." He is ever ready to dart into his burrow, 

 and if danger threatens he quickly retreats into this refuge. If 



