448 SUB-PHYLUM UROCHORDA OR TUNICATA. 
is usually complex, and forms the so-called dorsal tubercle, which 
is very distinct on the wall of the pharynx. It lies at the point 
where the two halves of the ciliated groove, or peripharyngeal band, 
already described, converge dorsally to form the dorsal lamina. In 
Ascidia the sub-neural organ is ventral to the brain, and partly 
RU 
STULANRUNLAN 
A LAN 
a: 
Fic. 241.—Diagram of Ascidian.—After Herdman. 
The arrows indicate the two openings; the dark border the test. 
Ph., Pharynx, with gill-slits; G., reproductive organs; H., 
heart, with blood vessels; G.D., genital ducts; &., rectum, 
ending in cloacal chamber. Surrounding the pharynx the 
peribranchial cavity is shown. 
glandular in character, and so it is in many; in some cases, however, 
it is dorsal in position, and its glandular portion is reduced to nil, 
It is probable that the sub-neural gland and its duct correspond to 
the olfactory pit of Amphzoxus, and perhaps to the hypophysis of 
Vertebrates. 
