NoTT. — On N.Z. Composite Ascidians. 309 



nised by a slight greyish tinge above the body of the animal. 

 The arrangeiiient is irregular. 



The branchial pores are extremely small, and are in most 

 instances quite indistinct. In specimens killed by Elsig's 

 method they are visible as faint dots on the white ground, but 

 in all other instances are inconspicuous till highly magnified. 

 As seen in transverse section under the microscope, the 

 aperture (fig. 5) appears faintly trilobed, the branchial siphon 

 (br.s.) being quite plain-edged. A well-marked branchial 

 sphincter (spJi.) surrounds the anterior end of the siphon. 

 The mantle has separated from the test in fig. 5, the limit of 

 the latter being seen as a faint ring (t.l.). 



The common cloacal openings are small and indistinct, 

 none being seen on taking a surface-view, though met with at 

 rare intervals in longitudinal sections. Cloacal canals are 

 well developed in the upper layer of the test (fig. 2, ex.), and 

 numerous canals of large extent are also present in the lower 

 layer below the zooids, communicating in many cases with 

 the cloacal canals by large passages. These lower canals in 

 some cases open on the under-surface of the colony (fig. 2), 

 where the great accumulation of faecal pellets suggests their 

 acting as common cloacal openings. 



The spicules (fig. 8) are fairly large, with sharply-pointed 

 rays varying somewhat in number and size. In distribution 

 (fig. 1) they are very numerous on the upper surface, and only 

 slightly less numerous through the remainder of the test. 

 Each is enclosed in a delicate membrane, which stains slicfhtlv, 

 in decalcified sections, with borax-carmine. 



Histologically, the test shows very numerous test-cells, 

 which stain deeply with carmine. They are rather smaller 

 and more numerous in the upper layer of the test, fewer and 

 larger below. Under a high power (E) they are distinctly 

 nucleated, and exhibit delicate fibrils, which sometimes ana- 

 stomose (fig. 6). No bladder-cells are met with. 



Test- vessels, in the form of vascular prolongations of the 

 mantle, are frequently met with, being sometimes furnished 

 with a terminal knob. Usually long and filamentous, they can 

 be here and there traced up to their point of origin from the 

 oesophageal region (fig. 2, v.ap.). 



The zooids are small, and very distinctly separated into 

 the so-called "thorax" and "abdomen" by a peculiar 

 oesophageal constriction (fig. 2, cb.c.) just above the abdominal 

 portion of the oesophagus, and below the vascular appendage. 

 The abdomen slightly exceeds the thorax in size (fig. 10), and 

 in decalcified specmjens is usually found to have shrunk away 

 from the wall of its test-cavity, leaving the mantle-epithelium 

 and connective tissue of the mantle round the zooid, while the 

 mantle-ectoderm (fig. 4, m.e.) is still attached to the test. 



