NEW DARWIN HALL GROUP - 249 



with tentacles, bristles and spines. The chimneys of their houses project 

 above the sea bottom here and there, while our license as group-makers 

 permits us to expose and section their burrows to show the inhabitants 

 therein. 



Driven to dig and burrow and to build underground homes for them- 

 selves, the inhabitants of the mud and sand have preserved their race from 

 extinction by thus concealing their soft bodies from their mortal enemies 

 the heavily armored crabs and swift-moving fishes which hold supreme 

 power in the water world above. But even in the mud the struggle for 

 existence goes on. Many of the worms are predacious and actively prey 

 upon their fellows. Some of the larger moUusks like the sand-collar snail, 

 dig rapidly through the soil and seize upon the worms in their burrows. 

 They are not even safe from the attacks of fishes, for scup and tautog 

 eagerly root in the mud for them. Hence the worms have been driven to 

 all sorts of protecting and concealing devices, to hinder or prevent these 

 attacks. Many build tubes and shells for themselves, and in the course of 

 time have adapted their form to their habitation so that they can live in 

 no other way. 



Let us examine the group more closely for examples of these various 

 adaptations. To the left among the eel-grass roots, a cavity is represented 

 arbitrarily hollowed out to disclose the worms burrowing there. The pre- 

 dacious clam worm {Nereis vireiis) actively wriggles from its burrow and 

 with powerful jaws viciously attacks its nearest neighbor, the long and 

 slender opal worm {Arabella opalina), so-called from the changing opalescent 

 hues of its many body rings. Beak-throwers {Rlu/nehobulus dibrauchiatus) 

 swim about them with a curious corkscrew motion, and suddenly shoot 

 forth a club-shaped proboscis armed at the end with hooklike jaws. 

 These are all actively moving species. Their many segments are similar 

 and furnished with similar segmental limbs throughout, and to this extent 

 they probably represent the structure of the primitive ancestral type of 

 this general group. 



They must be contrasted however with their tube-dwelling relatives 

 such as the plumed worm {Diopatra cuprcsa) which builds deeply penetrat- 

 ing tubes, the outstanding chimneys of which are protectively concealed by 

 the shell and weed fragments cemented about them. One of these tubes is 

 shown in section, disclosing its occupant, whose blood-red gill plumes and 

 segmental limbs are well developed on the forward portion of the body, 

 where they are near the tube-opening, but are reduced to small rudiments or 

 are altogether wanting on the hinder extremity. This is a partial adapta- 

 tion to the tube-dwelling habit. 



The most marked case of adaptation however is that of the parchment 

 worm {Chcetopferus vario pedatus) the f'-shaped tubes of which are shown 

 in the center of the group with their chimneys extending above the sea- 



