EEPORT ON THE TUNICATA. 
117 
looking. The head varies in its thickness from 1 cm. a short distance above the 
peduncle to O'o cm. at the upper end. One surface of the head is much more convex 
than the other, but this is probably an individual variation. 
The peduncle is strong, and is almost circular in section. It is narrowest a 
little below the base of the head, and then expands slightly towards its lower end 
(PL XYII. fig. 1). The actual point of attachment is not present in the specimen figured, 
but must have been immediately below the torn end. The peduncle is entire in the 
other specimen, and is somewhat irregular in form at the point of attachment. 
The general colour of the colony is a light grey, but the head has a slight but warm 
yellowish tinge, except at the very base, at the uj^per end, and along a series of lines 
which run vertically between the rows of Ascidiozooids. At these points the colour is 
still grey, or even in places white, and is seen on a close examination to be due to a 
large number of small rounded masses of opaque white pigment imbedded in the test. 
This pigment is most abundant at certain points between the rows of Ascidiozooids, and 
at the top of the colony (PL XVII. fig. 2), and is present in much greater quantity in 
one of the specimens than in the other, thus making a considerable difference in the 
external appearance of the two colonies. The surface is not perfectly smooth, but appears 
to be very finely roughened (PL XVII. fig. 8). 
The Ascidiozooids are clearly visible on the surface of the colony (PL XVII. fig. 1). 
They show as opaque yellowish-grey areas about 1 mm. in diameter. They are smallest 
at the base of the head, and increase in size as they are traced upwards. They are 
arranged with great regularity in vertical lines, and these rows are placed in pairs, each 
pair being separated from its neighbours by ridges of test from 1 mm. to lA mm. in 
width. It is in these areas that the vertical bands of white pigment are developed 
(PL XVII. figs. 2, 8). In each pair of rows the Ascidiozooids are placed alternately so as 
to form a zigzag line (PL XVII. figs. 1, 2). The longest row of Ascidiozooids is 2 '2 cm. 
from base to top. The bodies of the Ascidiozooids extend inwards nearly at right angles 
to the surface, but only occupy a zone about 1'5 mm. in width. The remainder of the 
head is formed by a spongy mass of test, penetrated in all directions by the vascular 
appendages of the Ascidiozooids. In a vertical section the lower part of the head and 
the peduncle are seen to be marked by delicate longitudinally running fibres. This 
appearance is due to the vascular appendages. The thoracic region of the Ascidiozooid is 
larger than the abdominal (PL XVII. fig. 9). It is nearly as broad as it is long, while the 
alimentary and reproductive viscera form a rather narrow mass elongated antero-posteriorly. 
As a whole the test is firmer than usual in this species. The outer layer of the 
head forms a strong but thin transparent membrane, in certain parts of which aggre- 
gations of white pigment are formed between the anterior ends of the Ascidiozooids 
(PL XVII. fig. 4,p.c.). The test of the .inside of the head is more tough and s|)ongy in 
its nature, and is rather opaque. The peduncle, although very much vacuolated, is firm 
