4S4 ON APPENDICULARIA FLABELLUM 



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

 animal. 



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

 server, published a memoir ^ on Appendicidaria, containing the results 

 of more extensive investigations than had hitherto been made. 

 Adopting the view that Appendicidaria is an adult form, Dr. Gegen- 

 baur constitutes four species of the genus, A. furcata, A. acrocerca, 

 A. cophoceira, and A. caridescens. The most important and novel 

 point in Dr. Gegenbaur's paper, however, is the discovery and de- 

 scription of the true branchial apertures, which had been overlooked 

 by all previous observers, Dr. Leuckart and myself included. Dr. 

 Gegenbaur says (1. c, p. 415) — 



■' If now we return to the branchial sac, the most remarkable 

 objects are the two respiratory clefts which lie on its ventral wall and 

 partially embrace the entrance into the cesophagus. Hitherto, none 

 of those who have investigated the Appendicidarice have recognised 

 the true import of these organs, although Mertens saw them in 

 Oikopleiira Ckaniissonis, and Busch (in Enrj/cerus padidas) would, in 

 all probability, have understood them had he only borne in mind the 

 typical structure of the Ascidians. Neither Huxley nor Leuckart 

 have mentioned these respiratory apertures.'' 



After describing the apertures, Gegenbaur proceeds — 

 " Exact observation shows that they are not simple apertures in 

 the branchial sac like those of the Ascidians, connecting its cavity 

 with the surrounding space ; but that each is prolonged into a short 

 tube which converges more or less towards its fellow on the ventral 

 face." 



In A. furcata these two tubes run 



" At first parallel with one another downwards (if the animal be 

 supposed to have its anterior part directed upwards, as in the figures), 

 then form a knee-like curve inwards, running directly towards one 

 another, and then entirely vanish, so that nothing more could be 

 made out as to their mode of termination. The function of the 

 respiratory apertures is therefore, in this case, entirely different from 

 that which they perform in the Ascidians, in which the water passes 

 through the branchial clefts, and, after aerating the blood contained 

 in the network of the branchial vessels, collects in the space between 

 the mantle and the branchial sac, to be eventually poured out of the 

 cloacal aperture ; while in our AppendiciUarice the water is led back 



^ Eemerkungen ueber die organization des Appendicularen, Siebold und Kollilver's 

 Zeitsch, B.VI. 



