90 ARTHUR BOLLES LEE. 



to the ciliated fossa. These points are shown in fig. 1 (s. o., 

 s. 0., the two sense-organs). 



By patient manipulation a living Salpa may be so placed 

 that an immersion lens may be brought to bear on one of the 

 sense-organs, and the points shown in fig. 2 may then, with 

 some care, be made out. The organ consists of a stem ter- 

 minating in a bulb, which is surmounted by a delicate hyaline 

 claviform appendage. The stem is seen to be a cellular 

 tube formed by a process of the inner mantle. (Ussow^s figure, 

 on the contrary, shows clearly that the author considered that 

 the inner tunica did not penetrate into the tube.) This tube 

 traverses the entire thickness of the hyaline outer mantle or 

 tunica, and swells at its distal end into the bulb. The bulb 

 seems, in favorable specimens, to lie simply in a cup-shaped 

 depression of the tunica. The lumen of the tube, in which the 

 nerve is frequently very clearly shown, is seen to be continued 

 for some distance into the bulb, and to expand there into a 

 cavity or vestibule (frequently somewhat more voluminous 

 relatively to the lumen of the tube than that shown in the 

 figure), in which the nerve breaks up into a delicate arbo- 

 rescence whose twigs terminate by means of small conical 

 swellings on the roof of the cavity (v. in the figure). From 

 the distal surface of the bulb delicate tapering hairs are seen 

 to arise by means of a conical base, and to be continued for 

 some distance into the claviform appendage. In the most 

 favorable cases they may be followed for about one third of 

 the length of this appendage, never further in the living state 

 (unless the specimens have been stained intra vitam with 

 gentian violet or the like). The appendage itself presents 

 but a single contour, is absolutely hyaline, and gives the 

 impression of being an extremely thin-walled tube or vesicle. 

 This is the view apparently expressed in Ussow's figure, but 

 we shall find that it does not answer to the reality. With 

 great care this single contour may be followed to the bottom 

 of the cup-shaped depression of the tunica spoken of above, 

 but is seen to be continuous there with the wall of this cup ; 

 so that the appendage is seen to be a papilla of the hyaline 



