REPORT ON THE TUNICATA. 91 



folds attached to the muscidar bands, this thin himiua is loose and hanf^s in bao-g or 



O O 



depressions. 



" In the bottom of each of these depressions is a slight three-cornered elevation 

 (PI. X. fig. 2), at the tip of which a perforation or aperture may possibly be present ; 

 but in the specimen examined such could not be made out. At the tip of each 

 small elevation were seen only three minute closely apposed villous folds of the 

 membrane, between which no aperture could be detected. The central horizontal 

 opaque white membrane is merely a thickened part of the general membrane, which is 

 spread over the muscular meshwork, and reaches to the tips of the large conical 

 processes. It is probably respiratory in function, and represents a gill. 



" The membrane was observed to be attached to the inner surface of the test- wall at 

 the intervals between the conical processes ; but the specimen was too much injured to 

 allow of the investigation of the extent and manner of its attachment within the 

 conical processes. It appeared to be attached laterally on either side to the inner walls 

 of these processes, and is probably reflected so as to line their cavities. No normal 

 perforated gill could be discovered in any part of this membrane ; but probably the 

 central thickened portion has a respiratory function, and possibly the eight small 

 elevations may prove to be openings. No reflection of the membrane over the inner 

 surfaces of the upper and lower walls of the test was observed. 



" The membrane was composed of an irregular mesh of fibrous tissue with numerous 

 rounded gland-like cells, and numerous nerves proceeding to the radial muscular 

 bands. 



" The mouth lies in the anterior part of the thickened portion of the membrane above 

 described, and at a short distance behind the inhalent aperture. Behind it is the 

 endostyle. The mouth is a simple oval aperture, encircled by a few sphincter muscular 

 threads. It leads directly into the digestive tract, which is embedded in a compact 

 nucleiform mass, which is seen conspicuously through the transparent test on viewing 

 the animal from beneath. The nucleus lies entirely beneath the horizontal membrane, 

 which is attached round the margin of the mouth. The exact arrangement of the 

 viscera inside the nucleus was not determined. A short tubular rectum projects fi-om 

 the anterior and inferior extremity of the nucleus. 



" Posteriorly to this, on the inferior surface, is a well-developed ovary, and behind 

 this, again, the testis. The ovary is a racemose gland, whilst the testis is composed of 

 short csecal tubes. In minute structure these organs agree closely with the testis and 

 ovaries of other Ascidians. 



"Between the mouth and rectum, in the middle line, lies the heart-shaped nerve 

 ganglion, immediately beneath which is a spherical body, which had the appearance of a 

 thin-walled sac full of a milky fluid. The wall of this sac is composed of a layer of 

 cells of rectangular outline, from the inner surface of which fine hair-lilie processes 



