360 LIVERPOOL MARINE BIOLOGY COMMITTEE REPORT. 



continuously behind the horizontal membranes from one 

 transverse vessel to the next. Koule, in his important work 

 on the Simple Ascidians of the coasts of Provence,* seems 

 to consider that these horizontal membranes, or transverse 

 vessels of the third order, are characteristic of Ciona intesti- 

 nalis, and also that they are always present in the branchial 

 sac of that species. The fact is that (1) the horizontal 

 membranes are present in many other species of Simple 

 Ascidians, and (2) that they are liable to variation in Ciona 

 intestinalis just as they are in other cases. I figure here 

 (PI. IX. fig. 6) a part of the branchial sac of a specimen 

 of Ciona intestinalis from the Isle of Man, which shews the 

 delicate vessels in question present in some meshes and 

 absent in others. 



The endostyle is not of much value as a diagnostic 

 feature. Its characters are very much the same in all allied 

 species. 



The dorsal lamina is of importance. In the different 

 species of the Ascidiidse it presents all intermediate con- 

 ditions between a plain broad membrane (the true dorsal 

 lamina) with a straight margin, and a series of long tentacle- 

 like languets. Ascidia plebeia is particularly instructive in 

 connection with these intermediate stages. This species has 

 a true dorsal lamina, but the membrane is crossed by trans- 

 verse ribs or ridges, and, at the margin, these are continued 

 into projecting teeth or processes. In some specimens the 



* Annates du Musee de Marseille, Zoologie, tome ii, Memoire No. 1, 

 1884. I take this opportunity of correcting an erroneous statement made 

 by M. Eoule in a footnote on page 212 of his work. In referring to wood- 

 cut fig. 9 of the first part of my Eeport upon the " Challenger" Tunicata, 

 he says that I have erroneously represented the viscera of Ascidia on the 

 right side of the body in place of on the left. That is not the case. My 

 figure represents a transverse section of the body, viewed from its anterior 

 surface. The top is dorsal. The animal's right side is on the observer's 

 left, and the viscera are placed on the left side of the branchial sac, as they 

 oucht to be. 



