REPORT ON THE TUNICATA. 
77 
Anatomy. 
The colony is somewhat club-shaped (PI. V. fig. 1), and may, for convenience of 
description, be divided into the stalk and the head. The stalk is attached by its lower 
extremity to some foreign body, and bears the head on its upjDer end. It is long and 
rather slender. It tapers downwards from the point of junction with the head 
to within a short distance of the lower end, where it spreads out to form a base 
of attachment (PI. V. figs. 4, 5). It is generally undulating in its course, sometimes 
twisted spirally, marked with faint longitudinal striae, and often wrinkled transversely 
(PI. V. fig. 1); in one or two specimens it is slightly constricted just below the head, 
thus forming a sort of neck. In colour it varies from light yellow (straw colour) to lio-ht 
reddish-brown. In a few specimens there is a collar or darker band of brown just 
below the head. Opaque yellow dots of varying sizes up to 0'5 mm. may be seen, 
especially if the stalk be held up to the light, in the interior. They are largest and 
most numerous at the upper end (see PL Y. fig. 10). 
The head is roughly ellipsoidal in form ; sometimes it is more of an oval, the pointed 
end being downwards. The investing mass between the Ascidiozooids is of a dull grey 
colour. There is always a patch of this to be seen, free from Ascidiozooids, at the 
summit of the colony. The Ascidiozooids apjDear externally as pale yellow blotches 
arranged in vertical lines. They are largest at the summit of the colony round the 
terminal bare patch, and gradually decrease in size as they are traced downwards to near 
the lower end. Here they rapidly get smaller, closer together, and less distinct till finally 
they are lost to sight at the top of the stalk. In some Ascidiozooids nothing more than 
the outline is visible, but in many a minute bright yellow opaque-looking dot is seen 
near the centre of the anterior extremity (PI. V. fig. 2). 
The head is essentially a mass of grey test, in the outer layer of which the Ascidio- 
zooids are imbedded. Its inner part is traversed by the vascular ajDpendages, which run 
inwards and downwards from the posterior or inner extremities of the Ascidiozooids. 
At the summit of the colony there are, as mentioned above, no Ascidiozooids, and of 
course no appendages, therefore in a transverse section of this region nothing but the 
grey test is seen. Here, however, it has generally a somewhat spongy, and, on the 
surface, ragged appearance (PI. V. fig. 2). 
In a section through the colony about the level of the top row of Ascidiozooids 
(PI. V. fig. 7) an irregular disk of grey test is seen, having a few Ascidiozooids and 
masses of embryos lying in its periphery, and extending in nearly to the centre. 
A transverse section about the middle of the colony (PI. Y. fig. 8) shows the same 
disposition of Ascidiozooids and of embryos in various stages of development, but here 
they only occupy the outer half of the disk, leaving in the centre a circular piece of grey 
substance which is more or less spongy as it is traversed by canals containing the 
