1892.] Development of Ciona, fyc. 513 



be regarded as the most primitive members of the order Ascidiacea, 

 rand that Botryllus and the Styelinse must take this position; for in 

 the structure and development of the pharynx, as well as in other 

 points, with which I shall fully deal elsewhere, the latter forms 

 approach, more nearly than any other Ascidians, the ancestral type 

 represented by Fyrosoma. 



V. " Observations on the Post-Embiyonic Development of Ciona 

 intestinalis and Ctavelina lepadiformis." By ARTHUR WlLLEY, 

 B.Sc. Lond. Communicated by Professor Ray Lankester, 

 M.A., F.R.S. Received May 4, 1892. 



The following is an account of some of the observations which 

 were made by the author during an occupation of the British Asso- 

 ciation Table at the Zoological Station at Naples from October, 1891, 

 to May, 1892. 



In their admirable " Recherches sur la Morphologie des Tuniciers," 

 (' Archives de Biologie,' vol. 6, 1887), Edouard van Beneden and 

 Charles Julin came to a number of conclusions which, while they 

 appeared to follow naturally from the facts observed, yet only added, 

 if possible, to the perplexity surrounding any attempt to regard the 

 Ascidians and Amphioxus from a common standpoint. Led away by 

 the remarkable behaviour of the endostyle which I observed and 

 described in the larva of Amjphioxus, I easily induced myself to accept 

 the views of the Belgian savants. 



The observations on the post-embryonic development of Ciona 

 described below oblige me, however, to reconsider the position 

 which I took in my paper on " The Later Larval Development of 

 Amjphioxus" (' Quart. Journ. Micro. Sci.,' vol. 32, 1891), with regard 

 to the mutual relations of the Ascidians and Amphioxus, and may, I 

 hope, tend to the establishment of reasonable homologies between 

 them. 



It is necessary to recapitulate very briefly the views of van 

 Beneden and Julin, in order to bring those which I am about to 

 oppose to them in the most striking contrast. 



The following table shows at a glance the homologies suggested by 

 the above-named authors : — 



(a.) The anterior intestinal di-~ 

 verticula of Amjphioxus, 

 the riffht one of which 



or, better, proboscis - 

 cavity, while the left 

 becomes the prseoral pit. 



-{ 



The primary branchial canals 



becomes the large head- )- = < of Ascidians {i.e., the first 



pair of gill-slits ; see below). 



