(ECOLOGY OF CIRRATULUS TENTACULATUS. . 67 
The best proof of the microscopic nature of the animal’s food is the ciliated 
condition of the gut. It remains to be seen by what means the animal is 
able to exercise selection. 
On the ventral side of the peristomium a deep groove leads back to the 
mouth and is continuous with the dorsal surface of the gut. On the walls 
of the pharynx immediately behind the mouth opening are situated a pair 
of flaps. These flaps are dorso-lateral in position and project each with 
its free edge standing out ventrally towards the median line (see Figs. 1-7). 
Gy. 
——— 
Fic. 1.—Transverse section Fig. ee ce section behind 
through the anterior portion Fig. 1, showing the development 
of the peristomium, showing of the sensory flaps. 
the ventral groove. 
Fig. 3.—Section through the peristomium, somewhat anterior 
to the line AB in Fig. 7. 
The two free edges are closely apposed and thus practically separate a 
groove above them from the remainder of the vestibule beneath. The 
epithelium of this groove and of the surfaces of the flaps which face 
inwards, including the free edges, is ciliated and rich in sensory elements, 
and is most markedly distinguishable from the general epidermis and from 
the lining of the vestibule, the floor of which projects forwards and seems 
glandular. The ciliated epithelium of the gut has already been noticed. 
The animal would thus seem to feed by a kind of suction ; the sensitive 
edges of the flaps being closely apposed would effectively prohibit the 
entrance of any but the smallest food particles, and these latter would be 
waited backwards by the cilia of the gut epithelium. 
