MOLGULA SIPHONATA. 55 



the accumulation of the branches; while the yellowish 

 brown colour of the test, harmonising well with that 

 of the zoophyte, renders the creature rather incon- 

 spicuous. 



The test (PI. XXVI, fig. 1, and fig. 42 in text), 

 though not by any means thick, is comparatively stout 

 for a Molcjula, and is tough and coriaceous ; the fibrils 

 (PL XL, fig. 2) are short and strong. 



The mantle (PI. XXV, figs. 4 and 5, and PL XXVI, 

 fig. 2) is thin and transparent, and on the left side 

 there are a few scattered, transverse fibres towards 

 the dorsal margin ; the usual radiating muscles at the 

 base of the tubes are not apparent, but whether from 

 deficiency or from obscuration is uncertain. 



The external surface of the branchial sac (PL XXV, 

 fig. 6) exhibits very distinctly the openings of the six 

 rows of pouches ; the orifices are long and narrow, and 

 are divided by the primary vessels. The gill-folds, of 

 which there are six on each side, are supplied on both 

 sides with three membranous rods ; and the secondary 

 vessels are arranged much in the same manner as they 

 are in M. conchilega, that is, between the folds they 

 show little disposition to form spirals, and run chiefly 

 in a longitudinal direction, though considerably curved 

 and undulated ; they assume, however, a spiral direction 

 within the margin of the folds, where the spirals are 

 arranged in pairs. The radiating vessels are numerous 

 and conspicuous, and rise boldly in relief from the 

 inner surface of the sac (PL XXVI, fig. 4). The oral 

 lamina is smooth, wide at the mouth, and narrowed 

 upwards. There are sixteen alternately large and 

 small, bipinnate tentacular filaments (PL XL, fig. 1); 

 they are a little apart, stout and large. 



The alimentary canal forms two loops, the lower of 

 which is wide, the upper narrow and not much pro- 

 duced ; the whole being placed towards the bottom and 

 ventral margin of the sac. The liver is composed 

 of fine laminae, which are regularly arranged on 

 each side of a median line ; the lobe of the right side 



