STUDIES ON THE PROTOCHORDATA. 295 



Studies on the Protocliordata. 



By 



Artlnu' Willey, B.Sc.Lrond., 



Columbia College, New York. 



With Plates 18—20. 



II. 



The Development of the Neuro-hypophysial System in Ciona 

 intestinalis and Clavelina lepadiformis, with an 

 Account of the Origin of the Sense-organs in Ascidia 

 mentula. 



(With Plates 18 and 19.) 

 While following the metamorphosis of the larva of Ciona 

 intestinalis last year (1892) in the Zoological Station at 

 Naples^ I noticed several peculiarities in the behaviour of the 

 nervous system which apparently could not be reconciled with 

 the account relating to Clavelina which was given by Ed. van 

 Beneden and Charles Julin in their work on ' Le systeme 

 nerveux central des Ascidies adultes et ses rapports avec celui 

 des larves nrodeles.' The first assumption to be made was 

 that the conditions might be different in Ciona from what 

 they were in Clavelina, as I had already perceived how much 

 the general development of Clavelina was modified in the 

 direction of a compression of the ontogenetic processes. But 

 on making preparations in toto of larvae of various ages of 

 Clavelina lepadiformis I could see, as far as the hypo- 

 physis is concerned, nothing at all like the appearance figured 

 by the above-named authors in their pi. xvii, fig. 11 (^ Archives 

 de Biologic,' t. v, 1884). Seeliger's figures of the larvee of 

 Clavelina are much more accurate in this respect (see I, 31). 



