ON THE ZOOLOGICAL STATION AT NAPLES. 345 



great extension of the works themselves. All who are acquainted with 

 the monographs previously issued and with the character of the research 

 involved will readily appreciate this circumstance. It is doubtful if any 

 other similar institution has produced so large a sei-ies of works as those 

 already published within the same time. 



2. Of the ' Mittheilungen aus der Zoologischen Station zu Neapel,' 

 vol. X., parts i. and ii., with 22 plates, have been published. 



3. Of the ' Zoologischer Jahresbericht ' the whole ' Bericht ' for 1890 

 has been published. 



4. Of the ' Guide to the Aquarium ' a new English edition has been 

 published. All four editions— English, German, Italian, and French — 

 are now illustrated. 



I. Report on the Occupation of the Table. By Mr. Arthur Willbt. 



I came to Naples with the object of studying Ascidian development 

 from the point of view of the close relationship believed to exist between 

 the Ascidians and Amphioxus. I had already made a study and pub- 

 lished an account of the post embryonic development of Amphioxus,^ 

 which revealed certain fresh points of contact between the two groups, 

 especially with regard to the behaviour of the endostyle. Having now 

 had an opportunity of making personal observations on the development 

 of some of the Ascidians, I have arrived at certain conclusions which 

 differ considerably from the position which I assumed in the paper above 

 quoted, and which I venture to think not only show the relations between 

 the Ascidians and Amphioxzis to be closer than was formerly supposed, 

 but also render them more intelligible. 



I attempted at the outset to obtain the embryos of Appendicularia, 

 bat after a long and wearisome search was unsuccessful, and accordingly 

 turned my attention to the embryonic development of the curious and 

 well-marked Ascidian, Gtjnthia papillosa, Linn., which spawned in the 

 tanks in the month of November. 



The eggs of this form are very opaque, and I had to make use of 

 transverse, horizontal, and sagittal sections. There is a considerable 

 quantity of yolk, and the gastrulation is preceded by what Davidoff calls 

 a 'plaknla-stage.' The mesoderm consists at first of an arc of cells lining 

 the posterior wall of the blastopore. It does 7<oi form a ring surrounding 

 the blastopore. It is easy to distinguish the mesodermal cells from the 

 endodermal on account of the practical absence of yolk in the former, 

 while in the latter cells the innumerable yolk spheres become very darkly 

 stained with osmic acid. The notochord arises purely from the endoderm, 

 and there is no question of a common ' Anlage ' of mesoderm and noto- 

 ehord. 



It is a curious fact that the eggs of this Ascidian only underwent 

 segmentation at night, just as is the case with the eggs of Amphioxus, 

 not that this is anything more than an analogy. Most of the young 

 tadpoles of this species, while still enclosed within the vitelline membrane, 

 instead of curving round ventrally, curved round dorsally. Whether it 

 was a pathological phenomenon or whether it occurred as a variation, I 

 cannot decide, but it is in any case interesting from the fact that the 

 dorsal curvature was almost invariably accompanied by what may be 



' See Quart. Journ. Microsc. Soi. vol. xxxii., March 1891. 



