146 DISCOVERY REPORTS 



arranged in double spirals meeting at the centre, the total number of turns being six or seven in large 

 stigmata. Some stigmata form unbroken spirals but others are broken at intervals. Radial vessels 

 (r.v.) numbering up to about twelve originate at the centre of each stigma, some of them passing 

 dorsally and some ventrally to join the corresponding vessels of the adjacent stigmata. The dorsal lamina 

 has an undivided border and becomes gradually wider towards the posterior end of the branchial sac. 

 Gut. The oesophagus is short and curved (Text-fig. 66 B, F, oe.), and the stomach (st.) wider than 

 the rest of the gut and about twice as long as wide. Its surface is marked with many low rounded 

 swellings. The intestinal loop is open only at its distal part. The rectum bends upwards and forwards 

 to end below the atrial siphon. The anus (a.) has a two-lipped opening. 



S. GEORGIA 



KERGUELEN 



FALKLAND IS 

 &. PATN SHELF 



CAMPBELL, 

 AUCKLAND &. 

 MACQUARIE IS 



ANTC CONTINENT 



GRAHAM LAND 



25 

 _J_ 



50 



— 1_ 



100 



-J 



SCALE # 



Text-fig. 67. Affinities of ascidian faunas in the Discovery Collections. Four of the corners of the figure represent the four 

 faunal areas: 1, Antarctic Continent; 2, Graham Land; 3, S. Georgia and 4, the Falkland Islands and the Patagonian Shelf. 

 In each area the percentage of species found also in the other areas is indicated by the height of the peak pointing to the 

 other area. Black polygons represent ascidian species. Clear polygons enclosed by broken lines represent sponge species 

 and are based on figures given by Burton (1932). 



Gonads. There is one gonad on each side of the body, that of the left side lying a little dorsal to the 

 gut, in the secondary intestinal loop. The right gonad (Text-fig. 66A, g) lies dorsal to the renal sac. 

 Each gonad (Text-fig. 66 G) is sausage-shaped or ovoid and consists of the ovary (ov.) extending the 

 whole length of the gonad, and the testis (t.) in the form of groups of follicles arranged round the sides 

 and ends of the ovary. There is a single short terminal oviduct (od.) and usually two male openings on 

 short tubes (s.d.), arising from the mesial face of the gonad. 



Renal sac. The renal sac is a short slightly curved body on the lower half of the right side (Text- 

 fig. 66 A, r.s.). 



Feeding mechanism. The branchial sac contains a mixture of sand grains, small inorganic particles, 

 whole and broken diatoms and small algal cells (PI. VI, fig. 6). Sand grains and most of the other 

 inorganic particles are, however, absent from the stomach and intestine (PI. VI, fig. 7) indicating that 

 there is some sorting mechanism. The mechanism is probably in the oesophagus which appears to 

 accept food particles and reject sand grains and other particles not of food value. The nature of this 

 mechanism is unknown, and its operation does not seem to depend solely on the size of the particles, 

 because diatoms are accepted which are as large as the sand grains that are rejected. Possibly the 





