AXATOMY AND DEVELOPMENT. 239 



a pelagic life, and have acquired the faculty of attaining 

 sexual maturity -- would be more in harmony with what 

 we know of the relation of Amphioxus to the Ascidians. 

 And it would seem that this affinity can be better demon- 

 strated through the comparison of Amphioxus, both adult 

 and larva, with a fixed Ascidian like Ciona than with 

 Appendicularia. 3 



On the latter view, therefore, the so-called metamerism 

 of the tail of Appendicularia, on which so much stress has 

 been laid, would be simply a secondary elaboration of the 

 tail for the purpose of serving as a permanent locomotor 

 organ. 



The dorsal nerve-cord of Appendicularia was regarded 

 by FOL as a simple peripheral nerve. We have described 

 above how a portion of the primitive nerve-tube in Ciona 

 and other Ascidians becomes reduced to a solid nerve. 



It would be of the greatest interest to discover the mode 

 of origin of this nerve-cord in Appendicularia. 



Abbreviated Ontogeny of Clave Una. 



In order to demonstrate clearly the relatively primitive 

 character of the development of Ciona it is sufficient to 

 enumerate a few facts drawn from the development of 

 Clavelina as described by Dr. OSWALD SEELIGER. As 

 mentioned above, Clavelina is a near relative of Ciona, and 

 in the adult condition resembles it very closely in many 

 respects. 



The development of Clavelina was formerly regarded as 

 being of a primitive character, but is in reality, more 

 especially in the later stages, abbreviated and hastened to 

 a remarkable extent. 



Like Ciona it possesses in the adult numerous trans- 

 verse rows of stigmata. Each opening, however, arises by 



