OF TUBULAR AND CELLULAR POLYPI, AND OP ASCIDIJi:. 379 



oval wheels revolving continually, in a direction ascending on the right and de- 

 scending on the left of each oval, as viewed from without ; but the cilise themselves 

 are very much closer than the apparent teeth, and the illusion seems to be caused 

 by a fanning motion given to them in regular and quick succession, which will pro- 

 duce the appearance of waves ; and each wave here answers to a tooth. The spaces 

 between the rows of spiracles are of much more substance than the intervals of the 

 spiracles : some ligaments/" are stretched from them across the side cavities to the 

 mantle, that seem intended to keep the branchial sac expanded. These spaces also 

 support finger-like processes e, about eight in a row, that project nearly at right angles 

 into the central cavity. 



The central cavity I shall venture to call the mouth, though the mouth is said by 

 CuviER to lie at its bottom. The large short tube at its opening ends in five or six 

 obscure indentations ; it can be drawn in and closed at the will of the animal, as 

 can the opening of the funnel. At the bottom of the tube the entrance of the 

 mouth is guarded by simple tentacula ^, some longer, some shorter, ranged sub- 

 alternately: their number was not ascertained. Whatever little substances, alive 

 or inanimate, the current of water brings, flow in unless stopped by the tentacula — 

 and they do not appear fastidious, — to the mouth; and lodge somewhere on the sides 

 of it. A lively animalcule will sometimes disengage himself by struggling, and dart 

 about in the cavity till he lodges on some other part ; or if a morsel is found un- 

 suitable, it is ejected by the funnel's being closed, and the branchial sac suddenly 

 contracted vertically. Mostly, however, whatever part the food lodges on, it travels 

 from thence horizontally with a steady slow course towards the front of the cavity, 

 where it reaches a downward stream of similar materials A; and they proceed 

 together, receiving accessions from both sides, and enter at last, at the bottom, the 

 oesophagus h! : this is a small flattened tube which carries them, flowing on in the 

 same way, without any effort of swallowing, towards the stomach : the tube takes 

 a sharp curve upwards and backwards before arriving there. 



It is extraordinary that these particles pass along in the mouth just behind the 

 spiracles, when the cilise are in full activity, without being at all affected by them. 

 I have in some positions seemed to catch a glimpse of a membrane suspended within, 

 too transparent to be commonly seen. One may imagine the water to pass to the 

 spiracles strained through the meshes of such a membrane, and the food to be carried 

 along it by invisible villi ; but this is mere conjecture. The projecting fingers have 

 the effect (whether intended for such a purpose or not) of detaining some prisoners 

 more bulky than the usual food of the animal ; for in several individuals I met with 

 small shrimp-like Crustacea confined between the rows : one escaped during an ob- 

 servation ; another after three days seemed as lively as when first swallowed. 



The stomach {i and i 2) runs backward horizontally ; its fore part had an inflated 

 look when seen from the side (fig. 2), and when from below (fig. 5) that of possessing 

 two lateral lobes. The food after accumulating here was observed to be pressed 



