W. K. BROOKS ON THE GENUS SALPA. 139 



the starting-point for the Tunicate phylum is to be found in a form 

 which was essentially like the modern Appendicularia, and that the line 

 which joins the Tunicata to the Vertebrate phylum must pass back- 

 wards from the Ascidians through the ancestors of Appendicularia to its 

 point of union with the Vertebrate line. 



In this opinion I fully concur, but before I discuss the remote ances- 

 try of the Tunicata, I wish to approach the subject from another point 

 of view, and to speak of the life-history of Salpa in certain broad rela- 

 tions to the question of the origin of the Metazoa. I shall then in 

 another chapter discuss the question of the degeneracy of the Tunicata 

 and the significance of the Appendicularia stage in their development. 



