W. K. BEOOKS ON THE GENUS SALPA. 203 



At present, however, the evidence all tends to show that the ancestors 

 of the tunicates had no such structure, and that the presence of coelomic 

 vesicles in pyrosoma is an adaptation to its peculiar mode of development. 



Since the critical review of the literature of the embryology of salpa will 

 require all tJie space which remains, I must bring this theoretical discussion 

 to an end, and must reserve, for publication at another time, the sections to 

 which I have referred, on the pelagic origin of the veiled medusae, and on the 

 morphological significance of metamerism and other vegetative duplications 

 in animals. 



