CHORDATA 435 
than many of the other members of Urochordata. Ciona 
intestinalis, which may serve as a type of this group, is 
abundant in the Mediterranean, and is found widely distributed 
in temperate seas. It is a hyaline transparent creature, when 
young presenting the appearance of opalescent glass, but as it 
grows old it is apt to become overgrown with foreign organ- 
isms, etc., and presents an opaque appearance. It attains a 
length of 5 or 6 inches. 
At one end the Ciona is attached to a rock or some other 
foreign substance, at the other end the mouth is situated, 
surrounded by eight lobed processes, this may be regarded 
as the anterior end of the animal. About an inch behind 
the mouth, and on that side of the animal which may be 
regarded as the dorsal, another aperture surrounded by six 
Fic. 252. — Diagrammatic 
section of part of mantle 
and test of an Ascidian, 
showing the formation of 
a vessel and the structure 
of the test. After Herd- 
man, 
m. Mantle. s, s’. Blood sinus in mantle being drawn 
e. Ectoderm. out into test. 
tc. Test cell. mc. Mantle cells. 
tm. Matrix. y. Septum of vessel. 
ble. Bladder cell. 
lobes is found; this is the atrial pore, and through this the 
water which has passed through the perforated pharynx and 
purified the blood, the waste matter from the intestine, and the 
generative cells are all discharged. 
The whole animal is enveloped in a hyaline ¢wnic or test, 
which is a cuticular excretion of the ectoderm, and into which 
ectodermal cells and blood-vessels wander. The test is turned 
in for a short distance at both the oral and atrial openings; at 
