MOLLUSC A, 205 



little substances, alive or inanimate, the current of water 

 brings, flows 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 dis- 

 engage himself by struggling, and dart about in the cavity 

 till he lodges on some other part ; or, if a morsel is found 

 unsuitable, 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, and they proceed together, receiving ac- 

 cessions from both sides, and enter at last at the bottom, the 

 oesophagus : this is a small flattened tube which carries them, 

 flowing on in the same way, without any effort of swallow- 

 ing, 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 ciliae 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, strain- 

 ed 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 pri- 

 soners 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 obser- 

 vation, another, after three days, seemed as lively as when 

 first swallowed. 



