ICHTHYOMENIA POROSA. 161 



The atrial opening is subterminal and opens into a comparatively large 

 sized cavity (Plate 5, fig. G) in which the ridges (Mundleisten) appear to have 

 no existence. On the other hand cirri are present in great abundance and in 

 some specimens project from the mouth for a short distance. These organs may 

 spring directly from the buccal wall, Ijut especially on the sides of the mouth 

 they are borne in groups of from three to seven on stalks containing muscle and 

 connective-tissue fibres between which there are extensive blood sinuses, enabling 

 the animal to project the cirri through the mouth opening. Each cirrus is an 

 unbranched process consisting of small cells with very indistinct nuclei and cell 

 boundaries owing to the large amount of yellowish brown pigment. In all of 

 the specimens sectioned numerous pigment granules have escaped from the cirri 

 and at various places form small accumulations, but whether this is a normal 

 process it is impossible to say. This secretion renders it also impossible to 

 determine their innervation, a difficulty that is increased by the small calibre 

 of the contained canal which in preserved specimens is too narrow to permit 

 the entrj' of blood corpuscles. 



The cirrus-bearing section of the digestive tract passes abruptly into the 

 succeeding region, the junction in every case being guarded by a distinct fold 

 which thus appears to be a permanent structure. At first the buccal-pharyngeal 

 walls are almost smooth and the epithelial lining, composed of cubical cells, is 

 thin but opposite the mid section of the brain the lumen narrow^s, becoming 

 trefoil shaped in section, and numerous small transverse folds have developed 

 which now are of greater thickness. This condition of afTairs continues with 

 slight modifications to the region of the ventral salivary glands where the canal 

 becomes increasingly narrower and the corrugations more pronounced. As 

 Plate 5, fig. 6, shows a clearly defined fold is present at the junction of the pharynx 

 and stomach. 



Throughout its entire extent the walls of the pharynx are thick and are 

 composed internally of heavy circular muscles to which are attached numerous 

 radiating bands in.serted on the other hand to the body wall. All signs of a 

 radula are absent and appearances suggest that this species like Drepanonicnia 

 vampyrella subsists on some delicate organism, such as the sea pens, whose juices 

 are extracted by powerful sucking movements of the pharynx. 



Two ventral salivary glands are present in the form of small tuliular out- 

 growths opening on the underside of the pharynx about ojiposite the level of 

 the hinder border of the brain. The cells are small but are filled with an abun- 

 dant secretion, indicating that though these organs are diminutive they are 

 functionally active. 



