390 Prof. J. Eeid on the Anatomy and 



only a very faint ash-colour, very different from the much deeper 

 ash-colour in all the dried specimens of Flustra avicularis I have 

 seen. 



These two polypes ought certainly to be classed as two differ- 

 ent species of the same genus, and not under two different genera. 

 A new genus should perhaps be instituted for their reception, as 

 their general character, and more especially the possession of 

 those remarkable appendices, the bird-head processes, separate 

 them from Acamarchis, Flustra and Cellularia, the genera to 

 which they are most allied. 



Pedicellina echinata. This polype is found in considerable 

 quantities in front of the Castle of St. Andrew and near low- water 

 mark, adhering to Cellular ia reptans, to Sertularice, and to the sur- 

 face of stones. It is more hardy than most of the other ascidian 

 polypes, and can be kept alive at home for a long time. The 

 number of tentacula varies from fourteen to twenty. In some spe- 

 cimens the stalk is nearly smooth, in others several spinous-look- 

 ing processes project from it, and in others both stalk and body are 

 covered with a long, fine and sparse down. In the young animal 

 the body is relatively longer and narrower. The body in the older 

 animal is very decidedly compressed from before backwards and 

 elongated transversely, and is considerably narrower and more 

 bulging at the edge in which the intestine lies (fig. 8 d) than at 

 the edge next the gullet (fig. 8 a) . The upper part of the body 

 is bounded by a slender rim to which the tentacula are attached. 

 This rim slopes slightly from the narrow towards the broad end 

 of the body. The tentacula at the extremity of the narrow end 

 are shorter than the others, and all of them become considerably 

 l^roader as they approach the rim. They are connected together 

 at their lower third by a contractile membrane, partly composed 

 of circular fibres. The body itself is not contractile. The inner 

 surface of the edges of the tentacula and the inner surface of the 

 rim are provided with strong cilia, and in the older animals the 

 external surface of the tentacula is frequently covered with a layer 

 of pretty large granules or cells. On examining the animal under 

 the microscope when placed in water containing a quantity of 

 carmine, the movements of the currents of water produced by the 

 cilia can be more distinctly observed. The two rows of cilia at- 

 tached to each tentaculum do not produce currents in opposite 

 directions, but both strike downwards and towards the mesial 

 line of the tentaculum to which they are attached, and cause a 

 current down the centre of its internal surface, by which the 

 particles of carmine are carried downwards to the rim. When all 

 the currents carried down the tentacula arrive at the rim, they are 

 rapidly conveyed along its upper edge by the action of the cilia 

 with which this portion of the inner surface is so abundantly 



