38 BRITISH TUNICATA. 



them ; in each fold there are from four to six. The 

 small transverse vessels distinctly radiate from the 

 centre of the spirals. 



In M. inconspicua the spiral disposition is reduced 

 to the minimum. The secondary vessels have most 

 generally a longitudinal direction, though they are 

 curved sufficiently to show that they are portions of 

 large compressed spiral coils, the centres of which are 

 lost to view in the pouches of the folds ; on each of 

 these there are four or five longitudinal membranous 

 bands obscuring their structure. The small, trans- 

 verse, radiating vessels are well developed. 



The oral lamina is a plain membrane, narrow above 

 and widening as it reaches the mouth, beyond which, 

 in M. conchilega, it passes downwards for some dis- 

 tance on the right side ; but it usually terminates near 

 the mouth. The branchial tubercle (PI. XLVIII, 

 fig. 1) occupies the usual place, immediately in front 

 of the upper extremity of the oral lamina. It is not 

 placed transversely as is usually the case ; but in this 

 genus is generally oblique with the involutions inclined 

 downwards. 



The endostyle is well developed, and forms a rather 

 wide groove from one end of the branchial sac to the 

 other, and is much arched, following the curvature of 

 the folds. Both the anterior and posterior cords are 

 well displayed. 



The tentacular filaments at the base of the inhalant 

 tube are always more or less pinnate or branched. In 

 M. conckiler/a there are eight or nine such filaments 

 with smaller intermediate ones. They are simply pin- 

 nate. M. simplex has about eleven, with a few minute 

 ones interspersed ; they are imperfectly tri-pinnate, 

 and have an irregular bushy appearance. In M. incon- 

 spicua they are less bushy, and the branches are more 

 regularly disposed; and in M. complanata they are 

 simply pinnate, the pinnae being few in number. 



The digestive organs lie on the right side of the 

 branchial sac, adherent to the pallia! wall, from which 



