210 GRAND STRATEGY OF EVOLUTION 



luscs ; and false radial symmetry is peculiar to the great 

 class of echinoderms, fig. 4. 



These two methods, as well as the pure radial type, 

 inevitably lead to serious mechanical difficulties in vital 



'-a. 



FIGURE 4. DIAGRAM OF THE METAMORPHOSIS OF A STAR-FISH LARVA, to 

 illustrate unequal bilateral growth and the conversion of an initial bilateral 

 symmetry into spiral symmetry and ultimately into the false radial sym- 

 metry characteristic of the echinoderms. 



administration, and it is not surprising that, in spite of 

 their immense antiquity, these three great classes of ani- 

 mals remain on a low level of organization, forever 

 handicapped by their constructive methods and ma- 

 terials. 1 



1 See "The Evolution of the Vertebrates and Their Kin." 



