BRITISH TUXICATA. 



branes much farther downwards than usual. The 

 collar of tentacular filaments at the base of the in- 

 halant tube is very near to the anterior margin of the 



v . O 



branchial sac ; and there are fifteen or sixteen rather 

 short filaments, with two or three minute ones between 

 them. But what is most peculiar in this species is the 

 deficiency of the branchial tubercle or any trace of it ; 

 we have examined three specimens and in not one of 

 them could we find this enigmatical organ so constant 

 in the Tunicata. 



The branchial membrane (fig. 13) is rather stout 

 and is minutely plicated longitudinally ; the primary 















- 



- 



' {\* ^ "* 

 ffli 



FIG. 13. Part of the branchial sac of Ascidla mamillata. Highly magnified. 



vessels are numerous and fine, Avith a few larger ones 

 interspersed. The longitudinal bars are also numerous 

 and less robust than the primary vessels with which 

 they form square meshes ; there is a large conical 

 papilla with the apex rounded, at each intersection, 

 and as the meshes are small the papillae have a rather 

 crowded appearance, especially as there is a small 

 papilla on the longitudinal bars, between each pair of 

 large papillae, and the membrane in connection with 

 the latter is short. The meshes or stomata of the 

 secondary vessels are of the usual rectilinear form, but 

 are less elongated than in many species. 



The reproductive organs are confined to the right 

 side of the body. The testicular caeca are spread over 



