REPORT ON THE TUNICATA. 



199 



The branchial sac has never large longitudinally running folds, such as are found in 

 the Molgulidae and Cynthiidse. The system of internal longitudinal bars is always 

 present, and is well developed. These tubes, by their intersection with the transverse 

 vessels, form the meshes visible on the inner surface of the sac (fig. 19), and at the 



l.v. 



il. 



><vvifvmf%jf 



V « 9 if if 



-tr. 



c.d. 



Fig. 19. — A Single Mesh of the Branchial Sac of Ascklia, seen from the inside. 



tr., transverse vessel ; i.l., Internal longitudinal liar ; l.r., fine longitudinal vessel ; p., papilla ; p 1 ., smaller intermediate papilla ; 



c.d., connecting duct ; sg. , stigma. 



corners of the meshes the internal longitudinal bars bear usually knob-bke projections or 

 papillae (fig. 19, p.) projecting into the interior of the sac. In some species {e.g., Ascidia 

 aspersa, 0. F. Midler, and Ascidia styeloides, Traustedt), these papillae are absent, or very 

 rudimentary; while in other species (e.g., Ascidia rneridioncdis, Herdman, and Ascidni 



l.v. 



Fig. 20.— Diagrammatic horizontal section through a Mesh of the Branchial Sac of Ascidia, showing the interior of the transverse 



vessel, connecting duct, and papilla at the right hand end. 



if., transverse vessel ; l.v., fine longitudinal vessel ; i.l., internal longitudinal bar ; p., papilla ; c.d., connecting duct; 



h.m., horizontal membrane. 



