730 IGERNA T,. .1. SOLLAS. 



sented in PL -34^ fig. 2. This external view shows at once 

 the character to which tlie generic name alludes, naincl}^ the 

 presence in the test of numerous ovoid fpecal pellets. These 

 are seen through the transparent substance of the test, and 

 now appear of an opaque cream-white colour. Clusters of 

 calcareous asters (fig. 3) mark out the oral siphons, since 

 they make a conspicuous snow-white patch around each 

 siphonal aperture. These white spots are visible also with 

 the naked eye. 



The arrangement of the ascidiozoids is irregular, A large 

 number of them share the same atrium, the atria being 

 shallow but extensive cavities with but few and small 

 siphons. The siphons are not visible in surface view, but in 

 section it is seen that their lips are formed of transparent 

 test-tissue destitute of spicules. 



The bulk of the common test, which consists of actual 

 tunicin, is small, its substance being excavated by numerous 

 oval spaces, in which the faecal pellets lie. To reach this 

 position the pellets must, after being ejected into the atrium, 

 sink through the excessively thin epithelial wall of that 

 cavity. The cellular elements in the test are of the usual 

 types; bladder- cells are specially abundant near both upper 

 and under surfaces, and round the oral siphons. Spicules 

 occur in small numbers, chiefly aggregated round the oral 

 siphons and in the neighbourhood of the branchial sac. 

 They may be isolated or packed in dense clusters (PI. 34, 

 fig. 3) . Finally the renal vesicles, described presentlj^, are to 

 be reckoned among the structures included in the test. The 

 ascidiozoids, as is common among Didemnida, have a sharp 

 constriction between the branchial region of the body and 

 the abdomen. 



The number of lobes round the oral siphons varies from 

 four to six. The tentacles are twenty-four in number ; 

 twelve long ones alternate with twelve short. The branchial 

 sac has four rows of five stigmata on each side. Connectives 

 (Hancock; trabccula3, Yves Delage) are absent. The 

 dorsal languets are long and median in position. The sub- 



