Miscellaneous. 337 



niuitt styUferum, Perophora *, and Amaroucium, likewise derives the 

 nervous system from the inner vesicle, although in a somewhat 

 different fashion. Consequently hoth in the forms alluded to and 

 in Botryllus the intestinal trart, the peribranchial cavity, and the 

 nervous system proceed from the inner vesicle of the two-layered 

 bud-rudiment. 



While, liowever, in the first-mentioned forms this inner vesicle is 

 endoderiuul, in Botnjllas it is, as has been shown, of an ectodermal 

 nature. 



As is evident from what has been stated above, these results of 

 mine are diametrically opposed to the conceptions of SeeUger t and 

 fcjaleusky. In the case of the buds of Clavtliaa and Pyrosuma J the 

 nervous system is derived by Seeliger from immigrant mesoderm 

 cells, while in the latter form it is stated by Salensky § to arise as a 

 thickening of the " outer vesicle." With the last-mentioned author, 

 however, I am so far in agreement in that I also have found a 

 common origin for the hypopliysis and the ganglion. 



II. 



The mode of formation of the ganglion in the buds of Botryllus 

 led me also to study the development of the same organ in the 

 larvae of compound Ascidiaiis. It will be seen from what follows 

 that owing to these investigations I have discovered several parallels 

 between the development of buds and larvae. 



In the cerebral vesicle of the larva of Distajjlia magnilarva there 

 appears at an early stage a difference between the left and right 

 sides. Nearly in the middle of the right side of the cerebral vesicle 

 there arises an evagiuation, which soon exhibits the most manifold 

 differentiations, acd from which in later development proceeds the 

 larval brain, which has been so exhaustively described by Yan 

 Beneden and Julin 1'. 



The left wall, however, in the meantime maintains its indifferent 

 cellular character : at first consisting of a single layer, it gradually 

 increases in thickness. 



In front of the described evagination of the right wall of the 

 cerebral vesicle the latter becomes tubular and joined to the intes- 

 tine. This anterior portion possesses cells of the same constitution 

 as that of those of the left wall. 



• Kowalevsky, " Sur le bourgeonnement du Perophora Listen" (transl. 

 by Giard), Rev. d. Sc. nat., Sept. 1874. 



t " Eibildung imd Knospung- von Clavditia lepadifurmis,'' Sitzgsber. 

 d. kais.-kgl. Akad. d. wiss. Wien, 1882. 



J '' Zur Entwicklungsgeschichte der Pvrosomen," Jenaische Zeitschrift, 

 23 Bd. 



§ " Beitrage zur Embrvonalentwicklung der Pyrosomen," Zoologische 

 Jahrbucher, 1891. 



I| " Le sysleaie nerveux central dea Ascidies adultes et ses rapports 

 avec celui des larves urodeles," Archives de Biologie, t. v., 1884. 



