148 



ZOOLOGY 



a double row of scales covering over the back (Fig. 134). 

 These scales are outgrowths of the dorsal part of the 

 parapodia, and serve for respiration. In allied 

 genera the scales are covered with bristles, 

 which may be so very long and abundant as 

 to hide the scales. They produce a brilliant 

 iridescence. One of these worms with the 

 great bristles may be several inches long and 

 relatively broad, and is commonly known as 

 the "sea-mouse" (Fig. 135). Both Lepido- 

 notus and the sea-mouse occur in out-of-the- 

 way places, - - crevices of rocks at low tide 



or fairly deep 

 water, - - so that 

 they are not com- 

 monly seen at the 

 seashore. 



The sedentary Polychaeta are 

 mostly smaller and less familiar 

 animals than the free-living 

 Polychseta, but they have an 

 interest for us in showing how 

 greatly modified an organism 

 becomes when it takes on a 

 sedentary life. Its swimming 

 appendages become rudimen- 

 tary ; its eyes are usually lack- 

 ing ; there is no protrusible 

 proboscis armed with powerful 

 jaws ; the gills become grouped 

 almost exclusively about the 



FIG. iai. Lep- 

 idonotus, the 

 scaled worm. 

 Nat. size. 

 Photo, by W. 

 H. C. P." 



FIG. 135. Aphrodite, a sea-mouse. 



r. i.).. r\imn>uiit5, A, Neil-mouse. i c 1 i ^ i 



Nat. size. From Johnston. u PP er end of the bod 7> wnere 



