280 STUDIES ON TUNICATA, 



stellate type are also present, but these are rare. Bladder and 

 pigment cells are absent. Vessels also are absent; their function 

 is probably subserved to some extent by the lacun?e in which the 

 spindle cells lie; one quite often sees the cells arranged in linear 

 series, apparently in actual contiguity, in which case their lacunae 

 must be continuous. 



The mantle is fairly strong; retractor muscle-bands only are 

 present, and these are all evanescent before reaching the posterior 

 end of the thorax. A sphincter musculature is present round 

 both siphons. 



The branchial sac (Plate xxv., fig. 9) is remarkably long and 

 narrow. There are eleven to thirteen rows of about twelve, long, 

 round-ended stigmata on each side. The ciliated border cells 

 present each a convex edge, so that the margin of the stigmata is 

 undulating. The transverse bars are wide and not provided with 

 membranes on the branchial aspect. 



The endostyle is simple and straight. 



The dorsal lamina is represented by languets equal in number 

 to the transverse bars (PLxxvi., fig. 4). 



The tentacles are about eight in number, simple, filiform, fairly 

 long and relatively stout. 



The dorsal tubercle is of circular form, apparently with a simple 

 aperture. 



Alimentary canal (PI. xxv., fig.9). — The oesophageal aperture 

 forms the greater part of the posterior boundary of the pharynx. 

 The oesophagus is thin-walled and short; it curves inwards and 

 junctions with the oval thick-walled stomach on its inner aspect, 

 beyond its anterior end. The wall of the stomach is neither 

 folded nor irregularly thickened. The gut presents three distinct 

 segments. The first, which may be regarded as the small intestine, 

 is a short segment, with thin, somewhat folded walls, which pass 

 backwards from the posterior end of the stomach. Following 

 this is the thicker-walled large intestine, a somewhat longer, 

 markedly stouter segment witli quite smooth walls, which forms 

 the posterior boundary of the abdomen, curving across from the 

 ventral to the dorsal side and somewhat to the right. Defined 



