MOLGQLA CITEINA. 63 



The branchial sac (PL XXVI, fig. 8, PL XXVIII, figs. 

 3 and 4) displays well on its exterior the mouths of the 

 branchial pouches, placed in not much curved longi- 

 tudinal rows. These orifices are large, oval, and pretty 

 equal in size, and the primary vessels are seen between 

 them radiating backwards. The folds a,re rather wide, 

 not much curved, and prettily marked by the spiral and 

 the primary vessels ; and their sides are supplied with 

 three widish membranous rods. The spiral arrange- 

 ment of the secondary vessels is not very obvious 

 between the folds, but becomes quite distinct within 

 them ; where the spirals are placed in pairs, two pairs 

 occupy each pouch formed or bounded by the large 



FIG. 46. Reproductive organs of Molgula citrina. Magnified. 



primary vessels. The oral lamina differs from that of 

 all the other species in being of nearly equal width 

 throughout; it is in fact rather narrower near the 

 mouth, instead of widening as usual. The branchial 

 tubercle (PL XLVIII, fig. 3) is in the form of a simple 

 loop opening downwards. The tentacular filaments 

 (PL XL, fig. 4) are twelve or fourteen in number, 

 bipinnate, irregular in size and well developed. 



The alimentary canal (Pl.XXVII, fig. 6; PI. XXVIII, 

 tig. 5) forms a simple loop, which, on reaching the 

 dorsal margin, turns upwards and becomes perpendi- 

 cular ; the stomach is very slightly marked, being very 

 little wider than the rest of the canal. The liver 



