ANIMAL REPRODUCTIONS. 291 
«membrane is inflected behind. ‘This peculiar 
* ftructure of the tongue feems to fupply the de- 
* fect of teeth; whence maftication is performed 
* by the aétion and refiftance between the palate 
“ and tongue. 
* Where the mouth and palate terminate be- 
‘hind, the cefophagus commences in the higher 
“ and pofterior part.of the ovular globe, and be- 
* tween the two falival ducts, which unite to the 
* globe by penetrating the cavity of the mouth. 
“ It is very narrow at the origin, but dilates fur- 
“ther down. It is of a light afh colour, and 
€ formed of a thin membrane longitudinally cor- 
*rugated, by which means it eafily dilates and 
© contracts. | | 
€ Above the anterior part of the globe is fome- 
* times found the brain, of a palifh colour, and 
“in a manner divided into two lobes, fig. 1, 1. 
* I fay fometimes, becaufe the brain of {nails is 
* moveable, and changes its place according to 
* the motion of the animal: at times advancing 
* before, and at times receding behind the ovular 
‘ globe above the cefophagus, efpecially when ‘ 
“ the {nail ftretches out of its fhell. This is ef- 
* fedted by means of mufcles traverfing the fides 
* of the brain, and admirably united te it by fe- 
* veral connected interwoven filaments. The 
“ brain is but about a line in breadth, and not 
* more than one and a half in length; larger, 
22 * however, 
