PARALLEL DIVISIONS 71 



amalgamation of parts to form the head, repre- 

 sent the maximum organic development within 

 the Molluscan phylum, and are therefore farther 

 removed from the highest mammals than is the 

 lowly Chiton, because the Mollusca and the 

 Vertebrata have been advancing along inde- 

 pendent parallel lines, and the cephalisation, with 

 its implied brain-power, is an act of convergence. 



FIG. 3. Parallel divisions of Echinodermata. 



The Molluscan and Vertebrate phyla, and 

 all the phyla, although their actual origins are 

 lost in Silurian darkness, may or must be sup- 

 posed to have diverged from a common base 

 in the first instance. This point is illustrated 

 graphically in Fig. 2 ; and the same principle of 

 primary divergence and secondary parallelism will 

 apply to each phylum (Figs. 3 and 4). Nothing 



