DEVELOPMENT OF ECHINODERMS 3287 



The direct development from the egg to the adult in these protected forms, 

 seems to show that the elaborate shapes of the various larvae have been developed 

 secondarily for the special purpose of transporting the young and aiding in the 

 dispersal of the species, and, therefore, that they are not relics of any ancestral 

 forms. There can, however, be little doubt that the echinoderms were originally 

 derived from some form or forms with a two-sided symmetry, and it is certainly 

 curious what a close resemblance their assumed primitive larval form presents to the 

 larva of Balanoglossus, the worm-like animal described on p. 2951 of the last volume, 

 and considered by many authorities to be in the ancestral line of the Vertebrata. 



