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THE WORM-LIKE PROTOCHORDATES 



Echinoderms appear to have been derived by a series of changes mainly correlated 

 with the assumption of their characteristic radial symmetry; while the Chordates 

 retained the original bilateral symmetry, at the same time undergoing certain 

 changes, into the consideration of which it will be unnecessary to enter in this 

 place. Still more complicated are the changes necessary to evolve Balanoglossus 

 and its allies from the ancestral form. Such of our readers as are desirous of pur- 

 suing further this interesting subject, may be referred to the works of the observer 

 last mentioned. 



A PYROSOMA COLONY. 



In life the colony assumes a horizontal position. 



