48 



BRITISH TUN1CATA. 



All the simple Ascidians that have come under my notice, 

 not even excepting Pelonaia, have a collar of tentacular fila- 

 ments situated at the base of the incurrent tube, some distance 

 above the entrance of the branchial sac (PI. Ill, and figs. 7-9 

 in text) ; indeed the distance in some species is considerable, 



FIG. 8. Tentacles of dona fascicularis. Highly magnified. 



and no instance has occurred in which they could be said to 

 be connected with the gill. They are usually linear or slightly 

 conical, and are rather numerous, except in Pelonn.ia, which 

 has not more than twelve or fourteen ; but in Mniynla and in 

 some of the other Cynthiadse they are branched or pinnate, 



A 



- ' ' 





. 9. A tentacle of Cynthia echinafa. Highly magnified. 



and are not very abundant. They, however, all agree in 

 being soft, delicate, hollow organs; and the simple ones, at 

 least, have the interior divided by a septum into two 

 longitudinal channels, so that the blood will circulate freely 

 through them [as seen in fig. 7] . They appear to be an out- 

 growth of the lining membrane, and are supplied with blood 



