ALIMENTARY CANAL. 85 



the lower segments of this anterior ramus, and of the 

 upper segment of the pedicel, are developed into strong, 

 downwardly-curved teeth : it is very remarkable that so 

 beautiful a structure should be extremely variable, as it cer- 

 tainly is in Acasta sulcata. 



Caudal appendages. — With extremely few exceptions, 

 these are present in all the Lepadidse and Verrucidse ; 

 whereas amongst the Balanidae they occur only in the two 

 species of Pachylasma, and in one species of Catophragmus; 

 these being the genera most closely allied to the Lepadidse, 

 and where, consequently, their presence might have been 

 anticipated. These appendages are seated close together 

 over the anus ; they are multiarticulate, each segment 

 being sub-cylindrical, with a few small bristles round its 

 upper edge. 



Alimentary Canal. 



I have not much on this head to add to what I have said 

 under the Lepadidse. As in that family, the strong internal 

 membrane of the oesophagus terminates in a remarkable, 

 bell-shaped expansion (PI. 26, fig. 3,/), which, as observed 

 by M. St. Ange, serves to keep the upper broad end of the 

 stomach expanded. The oesophagus is well furnished with 

 constrictor and radiating muscles for closing and opening 

 it ; and it is thus capable of a strong swallowing movement. 

 The stomach runs down to the lower end of the prosoma, 

 and then doubling back on itself extends to the anus. As 

 the prosoma is much elongated in Tubicinella and Xenoba- 

 lanus, so is the stomach of unusual length in these genera. 

 In several species of Balanus, the upper edge of the 

 stomach is surrounded by from six to eight casca ; these 

 caeca I ascertained, in Balanus perforatus, are branched, and 

 penetrate a considerable way into the body ; and some of 

 them at least expand a little at their extremities. Each 

 csecum, from the manner in which it retained fluid, must, I 

 think, be furnished, at the point where it enters the 

 stomach, with a sphincter muscle. In Tetraclita, Chtha- 

 malus, Tubicinella, Coronula, and Xenobalanus, there are no 

 caeca ; but in Xenobalanus and Coronula balcenaris, there 

 are longitudinal, approximate folds in the upper, broad end 



