ON APPENDICULARIA FLABELLUM 453 



just the existence of this caudal appendage which makes this form so 

 exceedingly interesting. 



" It has been long known that all the Ascidians commence their 

 existence as larvae, swimming freely by the aid of a long caudate 

 appendage ; and as in all great natural groups some forms are found 

 which typify, in their adult condition, the larval state of the higher 

 forms of the group, so does Appendicularia typify, in its adult form, 

 the larval state of the Ascidians. 



" Appendicularia, then, may be considered to be the lowest form 

 of the Tunicata ; connected, on the one hand, with the Salpm, and on 

 the other with Pelonaia, it forms another member of the hypothetical 

 group so remarkably and prophetically indicated by Mr. MacLeay, 

 and serves to complete the circle of the Tttiiicata." 



In 1854 Dr. Rudolph Leuckart published, among many other 

 valuable contributions to zoological science, a memoir on Appen- 

 dicularia (for a copy of which I am indebted to the courtesy of the 

 Author.)! 



In several points Dr. Leuckart's view of Appendicularia differs 

 from my own. 



1. With regard to the "oval finely-granulous masses " attached on 

 each side of the dorsal parietes, Leuckart states that they are by me 

 considered to be " probably the ovaries." My words, it will be 

 observed, hardly justify this assertion ; I merely stated that they 

 seem to be a further development of what Mertens calls the ovisac, 

 which is a very different proposition. Dr. Leuckart's own view of 

 these bodies, " that they are the earliest indications of the subsequently- 

 formed stigmata," p. 84, is one with which I am, like Gegenbaur, 

 unable to agree. In fact, as will subsequently appear, Dr. Leuckart 

 has overlooked the true branchial apertures, unless indeed what he 

 describes as the anus be one of them. The anal aperture, he states, 

 is " situated on the right side, near the middle line, and exhibits a 

 strong ciliary movement." Now, the anus is really in the middle line, 

 and the ciliary movement which it exhibits could hardly be thus 

 characterized, but, as will be seen below, the description would 

 perfectly apply to one of the branchial apertures. 



2. Dr. Leuckart failed to discover spermatozoa in the organ which 

 is described by me as a testis. Nevertheless, it will be shown by-and- 

 by that there can be no doubt that such is its real nature. 



3. Finally, Dr. Leuckart arrives at the conclusion that Appen- 



' Zoologische Untersuchungen von Dr. Rudolf Leuckart, ?Ieft. II. Salpen und 

 Verwandte. 



