ANATOMY AND PHYSIOLOGY. 53 



has been suggested by Professor Huxley*, chiefly effect the 

 decarbonization of the blood ; while this so-called gill will aid 

 in this operation in proportion to its vascularity : as must, 

 indeed, all the tissues bathed by the respiratory currents. 



The ganglion lies on the ventral side of the respiratory 

 cavity, between the lining membrane and inner tunic, a little 

 in advance of the ciliated band, and directly in front of the 

 anterior extremity of what we may now term the oral lamina 

 (the pseudo-gill). All the nei'ves are given to the walls of 

 the cavity in other words, to the inner tunic or mantle. The 

 anterior extremity of the ganglion is produced a little, giving 

 an appearance to the organ as if composed of two centres. 

 On the anterior surface of the produced extremity there are 

 three or four imperfectly formed black pigment specks, having 

 the appearance of rudimentary eyes, which, however, Professor 

 Huxley considers to be auditory capsules. 



The " languet," Avith its ciliated " fossa," is placed just in 

 front of the ganglion, consequently on the same middle ventral 

 line with it and the oral lamina; it is a long, tapering, conical 

 process, with a longitudinal groove which widens at the base 

 where it joins the fossa, over which it seems to straddle. 

 There can scarcely be any doubt that this is an organ of 

 special sense ; and it would appear probable that its office is 

 to ascertain the quality of the respiratory currents, and may 

 therefore be olfactory. Thus in function the " languet " would 

 seem to agree with the branchial tubercle so constant in the 

 other Tunicates [with the apparent exception of Ascidia 

 mamillata, in which it is inconspicuous] but it is, moreover, 

 homologically speaking, the same organ, as appears demon- 

 strated by its position in relation to the ganglion, the ciliated 

 band, and the pseudo-gill. Like the tubercle, too, it is a pro- 

 duction of the lining membrane; and, as indicated by the 

 longitudinal groove, like it, also,, the "languet" is probably 

 formed of tAvo portions or folds of this membrane. It must, 

 therefore, not be confounded, as it frequently has been, Avith 

 the tentacular filaments of the oral lamina in Clavelina, Pyro- 

 soma, and se\ r eral other simple and compound Ascidians. 



The homologies, however, do not stop here ; the clear anas- 

 tomosing vessels or tubes ramifying over the surface of the 

 intestine, described and figured by Prof. Huxley,t and sup- 

 posed to " represent a hepatic organ," or "a sort of rudimen- 

 tary lacteal system," are, there can be no doubt, the homologue 

 of the rudimentary liver before described in Ascidia and in 



* "Anatomy and Physiology of Salpa and Pyrosoma/' 'Phil. Trans./ 

 1851, pt, 2, p. 570. f Loc. cit. 



