"Wl THE NEW EVOLUTION ®^ 



firmly to the supporting surface. Then the mouth 

 and the associated structures move upward to a posi- 

 tion nearly or quite opposite the point of attach- 

 ment. This curious process takes place in the 

 feather-stars (fig. 43, p. 87) (but not in the other 

 echinoderms), in the barnacles (fig. 30, p. 47) (though 

 not in the parasitic barnacles or in the other crusta- 

 ceans), in most tunicates, and in certain other 

 types. 



A curious feature of animals as a whole is the recur- 

 rence of similar or comparable forms in widely differ- 

 ent groups. 



Among the single celled animals or protozoans 

 some are attached and more or less radially sym- 

 metrical, like Stentor and Vorticella. Others are at- 

 tached and form colonies at the summit of a stalk, 

 like Codosiga or Epistylis. Some, as Amoeba, are free 

 living and capable of locomotion, but are sluggish 

 and creep equally well in any direction. Still others 

 float about freely suspended in the water. Many are 

 elongated and more or less bilaterally symmetrical, 

 and swim with great rapidity. Some are naked, 

 while others form beautiful regular and complicated 

 shells of lime or other substances, or rough aggluti- 

 nated tubes of sand grains, or other forms of body 

 covering. 



Among the radially symmetrical animals some — 

 indeed most — are attached. Some of the attached 

 types form colonies on the summit of a stalk (fig. 7X, 

 p. 117), as the umbellularians. Others, as many sea- 

 anemones (figs. 4, p. 5; 79, p. 143), are free living and 



[15^] 



