6o CALIFORNIA ACADEMY OF SCIIiNCES. 



endostyle on the one hand or the dorsal lamina on the 

 other. Figure 13, pi. ii, represents one of the papilla; of 

 about the average size and shape. The lateral processes 

 are always present, and of varying length, each one some- 

 times nearlv equaling half the distance between the hori- 

 zontal vessels. I have, however, never found them con- 

 nected with the corresponding processes of the adjacent 

 series to form complete internal longitudinal bars, as is 

 said by Garstang, '91, to be the case in some instances in 

 P. Listcri, and as sometimes happens, as I have observed, 

 in P. viridis. There is considerable variation in the 

 lengths of the middle portion {f. fig, 13) in the different 

 papillae. In some cases it is relatively considerably longer 

 than in the specimen here figured, being nearly as long 

 as the lateral processes. The papillae and their processes 

 always contain a lumen continuous with that of the blood 

 vessel on which they are situated, as represented in this 

 figure; and the walls of the proximal, or convex sides 

 of the processes, are always thickest. The cells here 

 are large and round or even columnar, while those of the 

 concave sides are much smaller and often flattened. The 

 dorsal lamina is represented by a low ridge (fig. 21, pi. 

 ii, d. I.) scarcel}^ noticeable, even on sections. The lan- 

 guets, three in number, turned to the right, have been 

 sufficiently mentioned above. 



C. THE ENDOSTYLE. 



But little need be said about this organ, since it is so 

 similar to what has been abundantly described for many 

 other tunicates. Fig. 34, pi. iii, represents a cross sec- 

 tion of it. All the parts described and figured by Fol 

 ('76) for Salpa and other tunicates are here present, 

 though presenting some differences in details of structure. 

 These differences pertain chiefly to the two " interme- 



