78 BRITISH TUNICATA. 



the longitudinal ones are not very numerous and are 

 mostly confined to the anterior portion. The tubes 

 are very short, the anal being a little longer than the 

 branchial, the orifice of which is almost sessile. 



The branchial sac (PI. II, and PL XVII, fig. 1) is 

 coextensive with the mantle ; both extend consider- 

 ably behind the visceral mass and are reflected a little 

 upwards on the right side as in A. mamttlata, there 

 being a slight internal ridge across the posterior 

 portion of the test. The branchial sac is prolonged 

 for some distance* below the mouth ; the walls are 

 minutely, but distinctly plicated ; the primary vessels 

 are numerous and vary in size, the larger having 

 several smaller ones between them. The stomata are 

 rather long and wide, with the extremities rounded, 

 sometimes a little pointed. The papillae are conical, 

 well developed, alternately large and small, and the 

 papillary membrane is unusually ample; the branchial 

 bars are stout, with a widish membrane extending 

 along the inferior margin. The oral lamina (PI. II) 

 is continued from one end of the branchial sac to the 

 other, diminishing a little in width after passing the 

 mouth ; it is wide, strongly ribbed on both sides, and 

 has the margin pectinated in advance of the mouth ; 

 behind it the margin is smooth, or nearly so. The 

 belt of tentacular filaments on the left of the mouth 

 reaches to the bottom of the branchial sac, and is 

 strongly developed ; the filaments are closely set and 

 numerous, there being sometimes as many as seventy ; 

 they are wide at the base and pointed above. The 

 endostyle (PL II, PL III, fig. 5, and figs. 5 and f> in 

 text) extends the full length of the gill. The branchial 

 tubercle (PL II, and PL XX, fig. 1) is usually irregu- 

 larly rounded, with the extremities turned a little 

 inwards; but the organ is subject to great variation 

 in this species, the extremities sometimes bending in 

 one direction, sometimes in another, and varying in 

 length and extent of convolution. The tentacular fila- 

 ments at the entrance of the branchial sac are arrang-ed 



o 



