184 HUXLEY, ON APPENDICULARIA FLABELLUM. 



does Append icularia 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 Salpce, and on the other 

 with Pelonaia, it forms another member of the hypothetical group so 

 remarkably and prophetically indicated by Mr. MacLeat, and serves to 

 complete the circle of the Tunicata. 



In 1854 Dr. Rudolph Leuckart published, among many 

 other valuable contributions to zoological science, a memoir 

 on Appendicularia (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" at- 

 tached 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 propo- 

 sition. Dr. Leuckart's own view of these bodies, " that they 

 are the earliest indications of the subsequently-formed stig- 

 mata," 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 Ap- 

 pendicularia is a larval form, and not, as I had suggested, an 

 adult animal. 



In 1855 Dr. Carl Gegenbaur, a very careful and excellent 

 observer, published a memoir f on Appendicularia, containing 

 the results of more extensive investigations than had hitherto 

 been made. Adopting the view that Appendicularia is an 

 adult form, Dr. Gegenbaur constitutes four species of the 



* Zoolo^ische Untersuchungen von Dr. Eudolf Leuckart, Heft. IL 

 Salpen und Verwandte. 



t Bemerkungeu ueber die organization des Appendicularen, Siebold und 

 Kolliker's Zeitsch, B.VL 



