114 PEAKSE. 



During the summer of 1911, the writer worked among the 

 tropical fiddler-crabs that swarmed in the estuaries near Manila 

 and on the mud flats along Manila Bay. In some places these 

 little animals covered the beach in countless numbers. At low 

 tide their bright colors and active movements made them con- 

 spicuous objects that could not fail to attract attention. Five 

 species and 1 subspecies occurred in this locality, 5 of them 

 being abundant. In order of decreasing numbers those repre- 

 sented were: Uca forcipata (Adams & White?, de Haan),^ U. 

 marionis Desm. and U. rathbimie Pearse,^ U. marionis nitida 

 (Dana), U. annulipes (Latr.), and U. gimardi (Milne-Edwards). 

 The behavior of all of these species was similar. The observa- 

 tions described in the following pages were undertaken with the 

 purpose of discovering: (1) the habits and relationships of the 

 various fiddler-crabs inhabiting the estuaries of Manila Bay and 

 (2) the use or uses of the peculiar adaptations of the males. 

 They were made between May 1 and August 1 at the estuary 

 extending from Pasay to Georgia Avenue in the City of Manila. 

 This narrow, shallow estero, as such places are termed in the 

 Philippines, is about 3 kilometers long and is bordered by native 

 nipa-palm houses along a large part of its extent. 



GENERAL HABITS. 



The fiddlers of Manila Bay are diurnal. On bright days, 

 moreover, many more individuals are seen outside their burrows 

 than when it is cloudy, provided the mud be somewhat wet. In 

 order to ascertain whether they were active at night, the writer 

 went to a place at the edge of an estero where he had been 

 making observations in day-light for about a week, and where 

 the ground was thoroughly familiar to him. On this particular 

 evening, June 16, the sky was overcast with clouds, but though 

 rain threatened, the darkness was relieved somewhat by occa- 

 sional flashes of lightning and by the dim glow from the electric 

 lights of Manila. The writer stumbled to his station at 8.15 

 and sat quietly on the grass for fifteen minutes. Then he flashed 

 the light from an acetylene bicycle-lamp suddenly over the most 

 populous part of the estero. Not a fiddler was to be seen. The 

 light was shaded while five hundred seconds were counted, and 

 again flashed over the estero. No crabs were in sight, but a 



' The writer's thanks are due Miss Mary J. Rathbun who examined 

 these species. Acknowledgment is also due to Mr. Tom Jones, of the 

 St. Louis University School of Medicine, who drew the figures appearing 

 with this paper. 



