ECTEINASCIDIA AND THE CLAVELINIO&. 159 



and I find that the branchial sac of Perophora viridis* is 

 in a particularly interesting condition which forms a 

 transition to the group lontsining Ecteinascidia, and shows 

 at once the nature of the papillse of Perophora listeri. 

 P. viridis has well-marked papilliform connecting ducts 

 placed at intervals along the transverse vessels, just as in 

 P. listeri, but each such connecting duct bears at its free 

 end two long tentacular prolongations, one directed anter- 

 iorly and the other posteriorly, which are evidently 

 rudimentary or imperfect internal longitudinal bars. I 

 have found (ten years ago) the same condition before as an 

 abnormality in the branchial sacs of some Ascidiidse t 

 (e.g., Ascidia plebeia, Gorella japonica, and C. parallelo- 

 gramma), and have pointed out its bearing on the 

 formation of the internal longitudinal bars. So that these 

 two species of Perophora form a gradation from Clavelina 

 to Ecteinascidia : — first the connecting ducts appear in 

 P. listeri, then imperfect internal longitudinal bars grow 

 out from the free ends of the ducts in P. viridis, and finally 

 the adjacent ends of these outgrowths unite to form the 

 perfect bars of the species of Ecteinascidia. 



Perophora viridis has twenty tentacles of two sizes 

 placed alternately ; while P. listeri has forty tentacles of 

 three sizes, but not placed with perfect regularity, the two 

 larger sizes being in the main placed alternately, while 

 between each pair of these occur two very short tentacles. 



* I notice that Lahille has just described practically the same condition of 

 affairs in the branchial sac of his new species P. banyulensis. He apparently 

 does not know of Verrill's P. viridis as he makes no reference to that species, 

 and as he describes his form as being " jaune-verdatre " and having twenty 

 tentacles of two sizes it is not improbable that the two may prove to be 

 identical. 



tSee Challenger Report, Part I, 1882, p. 192 ; and "Fauna of Liverpool 

 Bay," Report L, 1886, p. 358, and PI. IX, figs. 1—4, and 8. 



