756 
ZOOLOGICAL LITBKATUKE. 
A wide vascular ring surrounds the mouth, occupying nearly the whole of 
the space between the lip and the base of the oral lobes. 
Radially, this ring gives oft’ five highly mobile, irritable and extensile 
tubular tentacles, one opposite each of tlie intervals between the oral lobes. 
The cavity of these tentacles is continuous throughout, and immediately con- 
tinuous with the cavity of the oral ring. Their wall seems to consist of a 
simple contractile sarcode-hiyer, studded with oval yellowish endoplasts. 
There is no definite difterentiation of a contractile fibrous tissue. Under a high 
power, however, the sarcode appears to have a longitudinal arrangement j 
this may possibly be due to motion among the particles producing a play of 
light. The walls of these tentacles are produced into numerous delicate 
tubular processes, their cavities continuous with those of the tentacles. 
These processes are arranged in three or four irregular longitudinal rows. 
They are extensile ; their walls when extended are extremely delicate, ti'anspa- 
rent, and apparently structureless. When contracted, two or three delicate 
' ring-like rugie appear on the walls of each. Each process is terminated by a 
minute three-1 obed slightly granular head. At the base of each of these 
processes there is a delicate crescentic leaf-like fold, slight!}^ granular, and 
most distinctly marked when the tentacle is retracted. When one of the 
extensile tentacles is wholly or partially retracted, it is thrown into obscure 
' transverse wrinkles, which give it at first sight the appearance of being- 
divided by a series of dissepiments. When the tentacle is fully extended 
these folds totally disappear. At the base of each of these five az3^gous 
tentacles” there is a conical thickening and enlargement of the sarcode-tissue, 
contracting outwards towards the tentacle which is continuous with its 
apex, and whose cavity passes through it to unite at its base with the oral 
vascular ring. This conical projection is the commencement of the young- 
arm. The azygous tentacle terminates it, and leads it out, as it were, up to 
the point of bifurcation. The tentacle remains persistent for some time in 
the angle between the first two brachial joints, and finally becomes absorbed 
and disappeai-s. These five azygous tentacles are the first of a system of 
extensile tentacles,” which are subsequently developed in very extended 
series as appendages of the radial and brachial tentacular canals. In almost 
all cases, as soon as the interior of the cup can be examined after its expan- 
sion, the number of extensile tentacles has reached fifteen ,- but, from the one 
or two instances in which the ten additional tentacles have been absent, 
there can be no doubt that they are developed somewhat later than the five 
already described. They arise in five pairs, one tentacle on either side of 
and slightly within the base of each of the azygous tentacles, which they 
resemble closely in character. They commence as minute ctecal diverticula 
from the canal which passes through the enlarged base of the azygous ten- 
tacle, and become rapidly developed into tubular prolongations. At this 
stage, when the cup is open, the fifteen tentacles are usually fully extended, 
curving over the edge of the cup in the angles between the oral lobes, in 
threes, the azygous tentacle somewhat longer in the centre, and one of tlie 
paired tentacles on either side. 
Interradially, opposite each of the oral lobes, there is a pair of short tubular 
tentacles, their cavities likewise continuous with that of the oral vascular 
ring. These tentacles appear simultaneously Avith the five azygous extensile 
tentacles, immediately on the expansion of the cup. They are flexible, but 
