HUXLEY, ON APPENDICULARIA FLABELLUM. 189 



is the lowest, and when the appendage and the body are 

 parallel, it is about opposite the end of the rectum. The 

 nerve here receives a coat of minute rounded corpuscles, so 

 that an oval mass, about l-300th of an inch long, is formed, 

 from whence numerous minute fibrils radiate. The other 

 ganglia contain not more than two to five such corpuscles. 



Gegenbaur states that if Appendicularia furcata be exa- 

 mined from the dorsal surface, an S-shaped cleft, ciliated at 

 its edges, will be observed to the right of the ganglion. The 

 cleft, which occurs only in this species, pierces the wall of 

 the branchial cavity, and puts it in communication with the 

 sinus system. 



Seeking for this " cleft " in my Appendicularia {flahellum — 

 cophocerca ?), I came upon a slightly different, but I have no 

 doubt, corresponding organ. This is a pyriform sac (q), about 

 l-800th of an inch in length, presenting at its wider end an 

 aperture with a produced lip, communicating with the 

 branchial cavity, and by its narrower extremity abutting 

 upon the ganglion. The sac was richly ciliated within, and 

 I have no doubt whatever that it is the homologue of that 

 " ciliated sac," whose existence under different forms appears 

 to be universal among the Ascidians. There is every reason, 

 however, to regard this as an organ of sense, and it never 

 communicates with the sinus -system, so that probably 

 Gegenbaur's statement may be regarded as an error of inter- 

 pretation. 



I could discover no transverse muscles in the caudal 

 appendage, but only an upper and a lower layer of longi- 

 tudinal fibres, between which the axis of the tail was enclosed. 

 Whether this central axis is a solid body, or a membranous 

 capsule filled with fluid, I cannot say, but it is assuredly 

 closed at both ends. Its closed and rounded proximal ex- 

 tremity is readily seen, and I feel confident that there is no 

 such communication between the heart and the interior of the 

 axis as Gegenbaur supposes. In the individual already 

 referred to, in which the spermatozoa were effused into the 

 general current of the blood, none entered the axis of the 

 caudal appendage. 



The discovery of the external openings of the pharyngeal 

 canal and of the true nature of the supposed "ciliated 

 cleft," appears to me to possess peculiar interest, in that it 

 eliminates those structural peculiarities hitherto supposed to 

 exist in Appendicularia, which were in discordance with the 

 general plan of the Ascidians. That an Ascidian should 

 have apertures in its pharynx, establishing a communication 

 between its cavity and the sinus system, would be a great 



