96 SHELL GALLERY. 
The remarkable Rhopdlcea neapolitana, from Naples, may be 
roughly compared to an hour-glass with a very long constriction. 
The test is smooth in the upper part, but knobby and encrusted with 
foreign bodies below. The upper or thoracic end contains the 
branchial sac, and the lower or abdominal portion the stomach, 
heart, and reproductive organs, the gullet and intestine traversing 
the whole length of the narrow central region. Although from its 
general structure Rhopalcea is a Clavelinid, it is not certainly known 
to produce buds. 
Perophora listen (Fig. 15) occurs in the form of little jelly-like 
transparent blobs rising by short stalks from a silvery thread-like 
stolon. Owing to their small size and transparency, it is possible to 
examine specimens alive under the microscope, the currents passing 
through the stigmata in the walls of the branchial sac, and the 
beating of the heart being distinctly visible. The rapid motion of 
the cilia surrounding stigmata gives the appearance of dark wheels 
all rotating in the same direction. The heart beats so as to drive 
the blood current so many times in one direction, and then after a 
short pause, in the reverse direction. 
The exhibited specimen growing on an oyster shell, is from 
Plymouth. 
Sub-order 2. — Ascidi^e Composite. 
The Compound Ascidians are fixed forms, which give rise to 
colonies by budding, the individuals being immersed in a common 
mass and not possessing separate tests. 
Although reduced to an extremely small size each individual or 
ascidiozooid of a colony possesses the same organs as a large Simple 
Ascidian, excepting that the former does not possess a separate test. 
Frequently the individuals of a colony are grouped into systems, in 
which the atrial orifices open into a common cloaca. The little 
ascidiozooids vary greatly in shape in the different families. In the 
PolycUnidce, for instance, they are long, the organs being so to speak, 
drawn out, and being arranged in three regions, the thoracic, ab- 
dominal and post-abdominal, the first region containing the branchial 
sac, the second the stomach, and the third the heart and repro- 
ductive organs. In the Distomidce, the body exhibits two regions, 
thoracic and abdominal, the heart and reproductive organs lying 
alongside of the stomach. The Botryllidce comprise only one region, 
the stomach and the other organs being situated by the side of the 
branchial sac. 
