~388 ZOOLOGY. 
Order 1. Ascidiacea.—As an example of Tunicates (Fig. 
386"), we will now study the internal anatomy of Boltenia. 
On examining the test of this Ascidian, which is mounted 
on a long stalk, the oral or incurrent orifice is seen at the 
insertion of the stalk, and the atrial or excurrent orifice on 
the same side near the opposite end. On cutting open the 
thick test and throwing the flap over to. the left, the deli- 
cate mantle or tunic is disclosed ; it extends a short distance 
into the stalk or peduncle. This thin hyaline mantle is 
crossed by two sets of narrow raised muscular bands ; the 
transverse fibres are arranged concentrically to the two ori- 
fices, so as to close or open them, the longitudinal ones curv- 
ing outward from the left side. 
Currents of sea-water laden with organic food pass into 
the oral orifice, which is surrounded by a circle of tentacles 
pointing inward, and thence into a capacious saccular bran- 
chial chamber within the mantle, which contracts at the 
bottom, where the cwsophageal opening is situated. The 
walls of this chamber, which is over an inch long in a good- 
sized specimen, and gathered into fringed folds, is sieve-like 
with ciliated perforations (compare Fig. 3867 e), making the 
walls like a lattice-work, the blood coursing through the ves. 
sels passing between the meshes of the sieve-like waiis. 
The cesophagus, which lies at the bottom of this branchial 
chamber, is also situated near the intestine passing over 
the anal end into the short stomach. The intestine is long, 
passing up to the insertion of the stalk, where it is held 
in place by muscular threads extending into the stalk and 
attached to the mantle; it then srddenly bends back and 
passes straight down to the vent, which opens opposite to 
the atrial orifice ; the end of the intestine is in part revolute 
and provided with a fringe of about twenty filaments. The 
liver forms a broad and flat mass of a bright livid green, and 
consists of three flat lobes each composed of eight or nine 
lobules, with very short ducts enveloping the inner aspect of 
the intestine. The ovaries are two yellowish, large and long 
lobulated masses extending nearly the whole length of the 
body, while the right one is a little smaller, and situated in 
the fold of the intestine. The atrium is that region of the 
