3S8 ZOOLOGY. 



Order 1. Ascidiacea. — As an example of Tunicates (Fig. 

 386'), we will now study the internal anatomy of Bollenia. 



On examining the test of this Ascidian, which is mounted 

 on a long stalk, the oral or inctirrent orifice is seen at the 

 insertion of the stalk, and the atrial or excurrent orifice on 

 ihe same side near the opposite end. On cutting open the 

 ihick 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 

 transTerse fibres are arranged concentrically to the two ori- 

 fices, so as to close or open tbem, 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 oesophageal 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-hke 

 with ciliated perfora'ions (compare Fig. 386' e), making the 

 walls like a lattice-work, the blood couising through the Tes 

 «els psssing between the meshes of the pieve-Uke walls. 



The oesophagus, which lies at the bottom of this branchial 

 •chamber, is also situated near the intestine passing over 

 ihe 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 suddenly 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, whUe the right one is a little smaller, and situated in 

 -the fold of the intestine. The atrium, is that region of the 



