STRUCTURE OF APPENDICULARIA. 389 
body-cavity which lies between the end of the intestine and 
the atrial or excurrent orifice; into this atrial region the 
feces, eggs, etc., pass on their way to and out of the atrial 
orifice. 
The simplest form of Tunicate is Appendicularia, which 
is tadpole-shaped, bearing a general resemblance to the larva 
of an ordinary Ascidian, so that it may be properly called a 
larval form. The Appendicularia isa pelagic animal, usually 
about one-half of an inch in length, found floating at or 
near the surface when the ocean is calm, and occurring in 
all seas a few miles from land or in mid-ocean. It swims 
by means of its large, long, broad, flat tail, the body being 
Fig. 3862.,—Anatomy of Boltenia.—Drawn by J. S. Kingsley from the author's 
dissections. 
oval or flask-shaped. In Appendicularia flabellum, as de- 
scribed by Huxley, the caudal appendage is three or four 
times as long as the body. The mouth leads into a large 
pharyngeal or branchial sac; a narrow oesophagus at the 
bottom of this sac leads to a spacious stomach, with two 
lobes, from the left one of which the intestine arises, curves 
and ends midway between the mouth and insertion of the 
tail. In the middle of the hemal side (that side in which 
the heart is situated and bearing the atrial opening) is a 
fold of the wall of the pharyngeal cavity called the endostyle, 
On each side of this endostyle is an oval ciliated aperture, 
