14 ORGANIC DEPENDENCE AND DISEASE 



iology than the oyster and very rarely attached solidly to 

 the sea bottom, yet the same degenerative effect upon the 

 animal has been produced by burying itself in the mud with 

 only the tips of the valves or a pair of fleshy tubes extruded 

 upward to reach the moving food supply in the water cur- 

 rents, while the burial helps out in large measure the de- 

 fensive purpose of the solid armature of the shell. The 

 clam is a much older creature than the oyster and in specific 

 functions it has, broadly speaking, degenerated less, but it 

 serves to bring out the important fact that the habit of 

 burial in the mud, from which it does not easily release it- 

 self and never for long, is tantamount to fixation and in- 

 volves the organic stagnation in which these creatures have 

 lain for ages which can not be counted. This is hardly the 

 place in which to restate well-known paleontological facts, 

 but such cases as these and the extensive catalog of like in- 

 stances must serve to remind us that such adjustments, 

 early formed and perduring through the ages, have been 

 attended with the least possible variation in proportion as 

 the adjustment is perfect. The longest lived of all crea- 

 tures, then, are those which have lived in most perfect 

 adjustment and in which therefore readjustment is most 

 hopeless. 



We have very direct evidence of the early formation and 

 long endurance of specific habits of life in these adjusted 

 dependents. The starfish of the Devonian age fed upon con- 

 temporary mollusks in the same way and by the same mode 

 of attack that the starfish uses today upon the oysters of 

 Long Island sound; surrounding the tightly closed valves 

 with their strong-armed rays, pulling steadilj'' against the 

 strained muscle contraction of the mollusk until the weary 

 shell-fish, muscularly tired out, gives up, the valves relax 

 and open and the extrusive maw of the radiate enters.^ 



1 Clarke. Jour. Acad. Nat. Sci., Philadelphia, v. 15, 2d ser. Centenary num- 

 ber. 



