ON THE DIPLOCHORDA. 485 
pharynx as a pair of long channels (pl.), which are distin- 
guished by an absence of cilia. 
All these structures may now be followed in sections. 
Figs. 1 to 4 are a series of coronal or horizontal sections 
through Tornaria. The circum-oral and extra-oral areas 
are easily traceable through the depression of the former 
into the body of the larva and its very thin limiting walls. 
Fig. 1 is ventral to the mouth, and shows the circum-oral 
area crossing the ventral surface of the larva as a V, with the 
apex directed forwards. The anterior part of the circum- 
oral band (c.o.a.) is cut in four places, and the extra-oral 
band twice (ea.). 
-In the middle line the circum-oral area becomes the 
vestibule, and its roof, or dorsal wall, is seen to be slightly 
thickened. ‘The posterior part of circum-oral band is cut in 
its length across the floor of the. vestibule, and in two other 
places (c.o.p.) the dorsal wall of the vestibule is thick, and 
often carries small cilia. 
In Fig. 2 the edge of the mouth itself is cut. The thick 
dorsal and ventral walls of the pharynx are seen, and the 
left lateral groove (J.g.) is continued outwards into the 
circum-oral area. The right side is cut further back, and 
the lateral groove is no longer in communication with the 
circum-oral area. 
In Fie. 3 the pharynx is cut nearly in cross-section, and in 
Fig. 4 it is seen to join the stomach. 
Figs. 5 to 9 are a series of sections of the pharynx more 
highly magnified. Fig. 5 shows the lateral groove open on 
the left side and closed on the right. This and the following 
sections show the histological characters of the pharynx. It 
consists throughout of a single layer of cubical elongated 
cells. In the dorsal and ventral parts these cells carry cilia, 
but those surrounding the lateral grooves have none. ‘These 
cilia are far shorter than in the living larva, and have 
either contracted considerably or have been broken off. The 
lateral grooves show a number of clear vesicles or vacuoles 
arranged rather indefinitely, and varying 1n number accord- 
