THE WORMS 79 



form great stony masses, sometimes several feet in diam- 

 eter. 



74. Effects of an inactive life. In many species such a 

 sedentary life has resulted in the almost complete disap- 

 pearance of the lateral appendages, which therefore no 

 longer serve as organs of respiration, and this function has 

 'been shifted accordingly on to other structures. These 

 new organs are situated principally on the exposed head, 



FIG. 45. Sedentary tube-dwelling marine worms, upper left hand Sabella (one-half 

 natural size), the remainder Serpula (enlarged twice). From life. 



and Fig. 39 shows the general appearance of some com- 

 mon species. The corners of the mouth have expanded 

 into great plumes, sometimes wondrously colored like a 

 full-blown flower, and these, bounteously supplied with 

 blood-vessels, act as gills. When disturbed, the plumes are 

 hastily withdrawn into the tube, and some of the so-called 

 serpulids (Fig. 45, bottom of figure) close the entrance with 

 a funnel-shaped stopper. While the plumes are primarily 

 respiratory organs, they also act as delicate feelers, and may 

 even bear a score or more of eyes ; and in addition, being 



