390: 
ZOOLOGY. 
corresponding to the numerous branchial slits in the other 
ae 
aS 
[ATO 
arma 
SS AS 
Fig. 3808, — Struc- 
ture of a compound 
Ascidian, Amara- 
cium. A, branchial 
sac; m, stomach ; &, 
intestine ; ¢, mouth ; 
o/, testis; 7 7’, effer- 
ent duct of the tes- 
tis; C, ovary; p, 
egg in the ba Re 
ity; p”, eggs the 
atrium ; 7, anus; 0, 
shows the site of the 
heart; 2, liver; e, 
openings in walls of 
branchial chamber. 
—From Macalisier. 
Ascidians, bus in Appendicularia each oral 
aperture leads into a funnel-shaped atrial 
canal, the open end of which terminates 
beside the rectum. 
The heart is a large pulsatile sac situated 
between the two lobes of the stomach. The 
nervous system is much more fully developed 
than in other Tunicates, and is constructed 
on the Vertebrate type, consisting first of 
a ganglion situated below the mouth on the 
side opposite the atrial opening and opposite 
the anterior end of the endostyle. This 
nerve-centre throws off nerves to the sides of 
the mouth, and from it posteriorly extends a 
long cord past the cesophagus to the base of 
the tail, thence it extends along one side of 
the axis of the tail (urochord), swelling at. 
regular intervals into small ganglia, from 
which from two to five small nerves radiate. 
On the cephalic ganglion a round ear-vesicle 
is attached. Behind the posterior turn of 
the digestive canal is the testis and ovary, 
the Appendicularia being hermaphrodite, as 
Fol claims, though the ovary is developed 
later than the testis. The Appendicularfa 
has no test, but secretes a fibrous envelope, 
which is at first gelatinous, loosely surround- 
ing the whole body, and allowing the creature 
the freest motion within its cavity. 
The general structure of an Ascidian may 
perhaps be more readily comprehended by a 
study of acompound Ascidian (Amarecium), 
which grows in white or flesh-colored masses 
on sea-weeds, etc. On removing an Ama- 
recium from the mass and placing it under 
the microscope, its structure can be per- 
ceived. The body is long and slender, as 
seen in Fig. 386°. The. mouth leads by the capacious bran- 
