-!4 BRITISH TTJNICATA. 



All this is very similar to what takes place in connexion 

 with the alimentation in the Lamellibranchs ; but in them the 

 lateral currents of particles are as well defined as the main or 

 central ones. 



Molfjula, and Savigny's first and second tribes of his genus 

 Cynthia, appear to be the only forms among the simple Tuni- 

 cates that have hitherto been described as possessing a well- 

 developed liver. This organ is always sufficiently distinct in 

 these groups, and usually presents a laminated structure, but 

 is occasionally composed of tubular tufts or lobes, the colour 



FIG. 2. Hepatic tubes and globular vesicles in Ascidia sordida. Highly 

 magnified ( in. object-glass). 



being generally of a dark olive-green. I find, however, a true 

 hepatic organ in all the other genera examined (namely Ascidia, 

 Xft/ela, Pelonaia, Clavelina, and Perophora), quite distinct from 

 that gland-like substance coating the alimentary tube in the 

 first of these forms, and which has occasionally been con- 

 sidered to subserve the hepatic function. 



This substance is of a very peculiar character, and it is diffi- 

 cult to say what its office really is. In all the Ascidix it forms a 

 pretty thick coating over the stomach and intestine, and is 

 composed of comparatively large globular vesicles with thin 

 reticulated Avails, each having a large, opaque, simple or com- 

 pound nucleus on one side (fig. 2). These vesicles have no 



