STUDIES ON THE PROTOCHOEDATA. 319 



which have fixed themselves to the surface of the water. 

 They attach themselves in this way to the surface-film of the 

 water in the glass, both isolated and in groups. 



If one of these newly fixed individuals be examined under 

 the microscope, a small globule of air is invariably seen to 

 occur at the end of the adhering disc. It seems extremely 

 probable that this is secreted by the cells of the disc. 



The larvae would also fix themselves to pieces of ulva at the 

 bottom of the glasses, but I found it more convenient to leave 

 out the ulva, and get them to fix at the surface. Once fixed, 

 the young individuals can be kept for weeks in the same water 

 covered up. They apparently, however, never attain their 

 full dimensions under these conditions ; in fact, it could 

 hardly be expected that they should, so that for very late 

 stages I was driven to the tanks, where a constant supply of 

 Ciona was kept. 



As for the embryos of Clavelina, they are to be taken, as is 

 well known, from the peribranchial cavity of the parent, but, in 

 contrast to those of Ciona, cannot be obtained all the year 

 round, as the colonies of Clavelina die ofi" about the month of 

 May. 



As for the preservation, the method which gave the best 

 results consisted in fixing the larvae of all stages was the solu- 

 tion employed by Davidoff in his work on the ' Development 

 of Distaplia magnilarva (8), namely, 3 parts concentrated 

 corrosive sublimate and 1 part glacial acetic, the shrinking 

 tendency of the former being thus neutralised by the swelling 

 power of the latter ingredient. 



1. Metamorphosis of the Larva of Ciona intestinalis. 

 Origin of Branchial Stigmata. 

 " In den letzten 20 Jahren," says Kowalevsky in a memoir 

 which has recently appeared (22), " habeu sichj sehr viele 

 Forscher mit der Anatomic und Entwickelung der Ascidien 

 beschaftigt und man konnte hofi'en, dass die raeisten Fragen 

 schon gelost sind, und doch erweist es sich, dass bis jetzt die 

 Hauptmomente der Metamorphose noch ganz unerklart sind," 



