188 HUXLEY, ON APPENDICULARIA FLABELLUM. 



stances, to discover the direction of the circulating currents, 

 but in one individual, the testis, having attained its full deve- 

 lopment, had broken up within the body, and the sinuses 

 were filled with dark masses of spermatozoa. The heart, in 

 full action, propelled these in a regular course up one side of 

 the caudal appendage and down on the other (Mailer has 

 already described such a current in his ' Vexillaria), forwards 

 on the haemal side, and backwards to the heart on the neural 

 side. This individual was particularly instructive also, 

 by affording corroborative evidence as to the nature of the 

 pharyngeal canals. Had these been in any way connected 

 with the sinus system, as Gegenbaur supposes, the sperma- 

 tozoa could hardly have failed to pass into them. Nothing of 

 the sort occurred however ; they passed round in the sinus 

 between the walls of these canals and the outer tunic without 

 the slightest extravasation, and their dark hue gave the con- 

 tour of the canals only a better definition than it had before. 



The testis was always present ; small, discoid, and appa- 

 rently attached by minute radiating filaments to the parietes 

 in the younger specimens, it assumed the bilobed form in 

 the larger ones, occupying a large space behind the alimentary 

 canal. Individuals with fully-developed spei'matozoa were 

 comparatively rare. In that just referred to, the spermatozoa 

 had rod-like heads, about 1 -7000th of an inch long, with 

 very long, delicate, and filiform tails ; and the testis was re- 

 duced to a mere transverse band, the greater part of its 

 substance having apparently been shed in the form of sper- 

 matozoa. Of a vas deferens I could find no trace. 



The rounded bodies (m) on each side of the branchial cavity 

 anteriorly, appeared sometimes to present an internal clear 

 cavity, and might then be easily mistaken for ova. But the 

 absence of any germinal spot, the uniformity in appearance 

 of their bodies, in all individuals hitherto examined, and 

 their position, are very great objections in the way of any 

 such view of the matter. 



I must confess that the evidence adduced by Gegenbaur 

 appears to me insufficient to prove that the bodies which he 

 describes in other Appendicularice as ovaria are such organs, 

 and for the present I think it is safest to conclude that the 

 female organs of Appendicidaria are unknown. 



With regard to the nervous system and the organs of sense, 

 the only additional observations of importance refer in the 

 first place to the caudal nerve, upon which I found at regular 

 intervals small ganglion-like enlargements (PI. X., fig. 4), from 

 which, as well as in their intervals, minute filaments were 

 given off to the adjacent parts. Tlie largest of these ganglia 



