108 Miscellaneous. 



peribranchial sacs, the results obtained by Metscbnikoff and Kova- 

 lewsky in the case of Simple Ascidians, and has consequently arrived 

 at the conclusion that the brancMo-intestincd cavity is of endodermal 

 origin in the larvae of Compound Ascidians, while it is a formation of 

 the ectoderm in their buds. 



In this particular case, therefore, I am unable to share Hjort's 

 opinion ; the larvae of Amaroncium Nordmanni and Fragarium 

 elegans * had already led me to the same results as the BotryUidae 

 and Simple Ascidians, as to the endodermal origin of the peri- 

 branchial cavity ; and herein I am in accord with Delia Valle t, 

 who studied Ascidia mentula. 



But if the epicardium is a formation of general occurrence in 

 Tunicates, it does not possess the property of blastogenesis in all of 

 them. This property is non-existent in the Simple Ascidians, in 

 which the epicardium surrounds the alimentary canal and simply 

 plays the part of peritoneum. In the Botryllidse the epicardium 

 exhibits the same arrangement as in the Simple Ascidians, but the 

 peribranchial wall, which, after all, is nothing but the foremost 

 portion of the epicardiac sacs, possesses the property of budding. 

 Finally, in the Polyclinida3 (Amaroncium, Circinalium, &c.), in 

 Clavellina and Perophora we know that the epicardium is extended 

 to the tip of the stolon or of the peduncle when it exists, and this 

 it is that, by dividing or proliferating in different ways according 

 to the particular group, gives rise to the enteric cavity of the new 

 buds. 



IV. — I have traced, in series of thin sections, the development of 

 the nervous system of the larva as well as of the fixed Ascidian, 

 and have succeeded in elucidating various points with reference to 

 the sensory vesicle, as to which Kuppfer and Kovalewsky were 

 unable to agree. 



The sensory vesicle never opens on the surface of the ectoderm, 

 as it was stated to do by Kovalewsky ; but at a very early period it 

 is brought into connexion with the anterior portion of the future 

 branchial sac by means of a very short tube, which still exists, at 

 the moment of fixation, in order to give rise to the vibratile organ. 

 This communication between the nervous vesicle and the branchial 

 sac is ^f variable duration in the different species ; it no longer 

 exists in Ascidia villosa at the time of hatching, any more than in 

 the larva3 of Amaroncium and Fragarium ; while in Cynthia morns 

 the communication is still very wide on the second day after 

 hatching. 



The nervous system of the adult is produced by that of the larva 

 before it commences to degenerate, and by means of a process which 

 recalls that which I have already described in the case of Fragarium 

 elegans and Amaroncium Nordmanni %. — Comptes liendus, t, exxi. 

 no. 5 (July 29, 1895), pp. 270-273. 



* ' Comptes Kendus,' February 25, 1895. 



t * Archives italiennes de Biologie/ t. ii. 1882. 



J * Comptes Rendus,' February 25, 1895. ^ 



