ORGANS OF DIGESTION. 361 



having their buccal aperture situate at the bottom of a deep 

 respiratory sac, through which the aqueous currents are con- 

 veyed, exhibit no prehensile nor masticating apparatus nor 

 distinct organs of sense connected with the mouth. Delicate 

 tentacular filaments (Fig. 88. c.), analogous to the palleal 

 tentacula so common and numerous in the conchifera, are 

 generally disposed around the interior of the ciliated branchial 

 orifice (88. a.), and also of the anal aperture (88. b) or of the 

 anus (88. i) 9 to guard these passages from the intrusion of 

 noxious bodies ; both these orifices serve sometimes for the 

 entrance and sometimes for the exit of the currents which 

 aerate the branchiae and bring food to the mouth. The oral 

 tentacula are wanting in the pyrosoma ; they are simple fila- 

 ments in the phullusia, and are ramified in some of the 

 cynthue. They are generally more simple around the vent and 

 around the anus than at the respiratory orifice, and in some 

 species small red ocular points are seen around both the 

 respiratory orifice and the vent. There are six of these red 

 ocular points around the vent, and eight around the branchial 

 orifice in the common soft transparent green-coloured ascidia 

 intestinalis of our coasts, and they resemble the rudimentary 

 eyes met with in many of the simpler forms of radiated and 

 helminthoid animals. The inner surface, and marginal 

 tentacula of the respiratory aperture, are ciliated to pro- 

 duce the currents, as in conchifera. The mouth, or entrance 

 of the oesophagus, generally forms an oblique transverse 

 aperture, with loose sensitive lips, at the bottom of the 

 respiratory sac, as seen in the cynthia (88. t/.), so that the 

 food arrives at that aperture directly from the respiratory 

 orifice, (88. #.), before the currents have passed out through 

 the minute ciliated perforations of the branchial cavity. The 

 short and wide oesophagus leads to a distinct gastric cavity 

 (88. h.) sometimes plicated longitudinally, and perforated at 

 its pyloric extremity with the orifices of the wide ducts from 

 the biliary follicles. No teeth, nor jaws, nor salivary glands are 

 perceptible at the entrance of this very simple alimentary 

 canal, but the stomach forms a distinct enlargement, even in 

 the lowest species, and the liver is nearly as constantly 

 observed under some follicular form, opening into its cavity 

 as in the stomach of conchifera and almost all the higher 

 mollusca. The pyloric portion of this simple membranous 



