52 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
back along the right side of the dorsal lamina to the 
cesophagus. 
The dorsal lamina is at its widest round the cesophageal 
aperture (Pl. II., fig. 4, oes.). It is more or less ridged 
transversely, especially on its convex left side, and may 
have marginal tags or teeth (Pl. IV., fig. 4), which in 
some Ascidians become long processes, the languets. In 
the living animal, the lamina has its free edge curved to 
the right hand side in such a manner as to constitute a 
fairly perfect tube along which the train of food passes. 
WALL OF BRANCHIAL SAC. 
Fig. 3, Pl. II. shows a small part of the wall of the 
branchial sac of Ascidia in which it may be seen that the 
bars containing the blood channels are arranged in three 
regular series :— 
(1) The “‘ transverse vessels”’ (t7.) which run horizon- 
tally round the wall and open at their dorsal and ventral 
ends into large median longitudinally running tubes, the 
dorsal blood sinus behind the dorsal lamina and the ventral 
blood sinus below the endostyle (see also Pl. III., fig. 10). 
(2) The fine longitudinal or ‘‘interstigmatic vessels” 
(l.v.) which run vertically between adjacent transverse 
vessels and open into them, and which therefore bound 
the stigmata. 
(3) The “internal longitudinal bars” (2.l.) which run 
vertically in a plane internal to that of the transverse and 
fine longitudinal vessels. ‘These bars (see PI. I1., fig. 3, B.) 
communicate with the transverse vessels by short side 
branches (c.d.) where they cross, and at these points are 
prolonged into the cavity of the sac in the form of hollow 
papille (p.). 
In some Ascidians (e.g. Corella parallelogramma and 
most of the Molgulidz) the interstigmatic vessels ure curved 
