294 



BULLETIN OF THE BUREAU OF FISHERIES. 



and the brush is more conspicuous in older individuals than in the young. The tufts 

 of seta which are found on the propodus of the young and adolescent males disappear 

 gradually with successive molts, until their places in large individuals are marked by 

 small pits. 



PLEOPODS. 



The pleopods of the male differ from those of the female (Fig. 269) in having only 

 the outer limb, or exopodite, developed. Both exopodite and endopodite are devel- 

 oped in the female. The exopodites of the female are somewhat longer and broader 



than those of the male. The 

 first endopodite is similar in 

 shape to the exopodite, but 

 the remaining three endo- 

 podites are bifurcate, and in 

 adult females they are 

 fringed with long setae upon 

 which the eggs are carried. 

 These bifurcate endopodites 

 are not colored, being com- 

 posed of white, flexible chiti- 

 nous material. The edges 

 are reinforced with scutes 

 from the undersides of which 

 the long setae project in 

 tufts. Some of these setse 

 are plumose and shorter 

 than the others which are 

 nonplumose. 



The exopodites appear 

 to the naked eye to be finely 

 ribbed. These ribs appear 

 under the microscope as 

 dense, granular masses, 

 along which at intervals are 

 groups of minute setae. All 

 of these groups of setae do not appear to be the same, some being composed of two or 

 three comparatively long setae and one seta which is short. The longer setae are seg- 

 mented and plumose, while the shorter seta is segmented and nonplumose. Nerve 

 fibers extend through these setae, which indicates that they may be sense organs, but 

 whether they receive tactile or chemical stimuli is not apparent. The bases of these 

 setae are flask shaped, the distal portion of the segment being greatly enlarged. 



Other groups of setae are composed of three or four short setae, none of which are 

 plumose. They may represent the remains of longer setse which have been broken off, 

 although their ends are rounded. 



Fig. 268.— Development of second pair of legs of spiny lobster, Panulirus arqus. 

 Natural size. a. second leg of mature male; 6. second dactyl of old male; c, second 

 leg of young male; d, second leg of adult female. 



