ANATOMY AND PHYSIOLOGY OF SALI'A AND PYROSOMA 43 



young than in the aduh Salpa, and frequently, but not ahvays, its 

 cells contain an oily matter. 



There would seem to be no clue either to the homology or to the 

 function of this elaeoblast. Without hazarding a conjecture, it may 

 be remarked, as a curious fact, that these animals, so remarkable for 

 possessing in the fcetal state a true though rudimentary placental 

 circulation, possess an organ which in structure and duration some- 

 what calls to mind the thymus gland. 



15. The nervous system consists of a single subspherical ganglion 

 (fl'), situated in the space between the inner and outer tunics, just 

 where the anterior and lower extremity of the hypopharyngeal band 

 joins the ventral paries. It gives off two delicate branches forward to 

 the " languet" (16), and a great many in all directions to the parietes 

 of the body. There were no branches traceable specially to the 

 mouth or towards the oesophagus. 



A delicate but strong vesicle attached to the anterior and lower 

 surface of the ganglion, and containing four subhemispherical cal- 

 careous bodies, with black pigment spots on their outer surface, 

 evidently represents the auditory vesicle and its otolithes in the 

 gasteropod and acephalous Mollusca : and a conical depression in 

 the outer tunic leading towards this auditory vesicle, would appear 

 to be intended to bring it into closer relation with the surrounding 

 medium, Plate XVI. [Plate 6] fig. 5. 



16. There would appear to be yet another organ of special sense, 

 composed of the " languet " (/) and the " ciliated fossa " {w), called 

 by E^chricht the " langliches organ." 



The "languet" (Plate XVI. [Plate 6] fig. 5) is a long tongue-shaped 

 or conical process, fixed by its base to the ventral surface of the 

 respiratory cavity where this is joined by the anterior extremity of 

 the gill, and for the rest of its extent floating freely in the respiratory 

 cavity : it is curved so as to be convex anteriorly and concave pos- 

 teriorly, and its anterior surface is marked by a shallow vertical 

 groove ; at the base this groove is wider, and where it becomes con- 

 tinuous with the surface of the respiratory cavity, it presents a narrow 

 median slit, which leads into a small purse-shaped cavity, flattened from 

 side to side and richly ciliated within, Plate XVI. [Plate 6] fig. 5 w. 



The posterior contour of this ciliated fossa is formed by a delicate 

 thickened band or filament, much more distinct in some other species 

 than in the present. 



It would appear probable that the languet and the ciliated fossa 

 subserve in some manner the performance of the gustatory function. 



17. From each .side of the base of the languet a narrow " ciliated 



