STRUCTURE OF APPENDICULARIA. 



199 



body-cavity which lies between the end of the intestine and 

 the atrial or excurrent orifice ; into this atrial region the 

 faeces, eggs, etc., pass on their way to and out of the atrial 

 orifice. 



The simplest form of Tunicate is Appcndicidaria, 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 is a pelagic animal, usually 

 about a quarter 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. 136. 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 hremal 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 are two oval ciliated apertures, 



