UNIVALVE MOLLUSCANS. 283 



polypes no nervous centre, but molecules every 

 where dispersed ; then the next form is a nervous 

 collar round the oesophagus ; next dispersed gan- 

 glions ; then a ganglionic chord ; and so on till 

 we arrive at a regular brain and spinal marrow 

 incased in a vertebral column. We may with rea- 

 son therefore conclude, that the organ of vision, 

 when first planted, would be a mere rudiment, 

 though sufficient for the animal's purposes, and 

 possessing few of the characters it exhibits when 

 arrived at its most perfect form ; these it keeps 

 acquiring, as it becomes more developed, or to 

 avoid misconception from nibbling critics, the 

 Creator keeps giving it more and more perfect 

 sight till he brings it forth, in all its glory, in 

 the highest animals. 



The most common in this country of these her- 

 bivorous Trachelipods, is the garden-snail, 1 but 

 the species whose history has been most copiously 

 related, is that called in France the Escargot? 

 which, though stated to have been originally 

 imported into this country, now abounds in some 

 parts of Surry and other southern counties. I 

 shall begin by giving some account of their 

 economical and then of their physical history. 



On the continent, especially in France, this 

 large snail, which is more than double the size of 

 our garden one, is used as an article of food, and 

 though said not to be easy of digestion, is very 



1 Helix hortensis. H. Pomatia. 



