History of Concholuyy. 247 



mary divisions or books, — hence shells are divided into the land, 

 fresh-water, marine bivalve, and marine univalve classes ; and the 

 mode in which these are subdivided more resembles the synoptical 

 tables which the French botanists now frequently prefix to their 

 floras, constructed without any regard to the affinities of the objects 

 they approximate, and solely intended to hunt down a species, than 

 what is usually understood by a system in natural history. 



So far as we remember (for his works are not all of them by us, 

 and years have elapsed since their perusal,) the manner in which 

 the shell is formed, and its relation to the snail, occupied no part of 

 Lister's investigations, but previous to his decease the true solution 

 of the problem was discovered by the illustrious Reaumur.* No 

 experimental inquiry had hitherto been made on the subject, and 

 the remarks in reference to it in conchological writers were scatter- 

 ed, vague, and hypothetical ; while the opinion of better informed 

 physiologists appears to have been that the shells were organized 

 parts of the animal, which grew and increased with the latter by 

 receiving nutriment and material from the body ; that there was in 

 fact nothing peculiar in the formation of shell, but that its growth 

 depended, like the growth of other parts, on the circulation of 

 juices within itself, and on the assimilation and addition of new 

 matter. Reaumur was never content with reasoning on a point 

 which experiment alone could solve, and with his usual ability 

 and success he instituted numerous experiments on the subject un- 

 der review. They were principally made on land snails (Helix,) 

 but not restricted to them, for by confining fluviatile and marine 

 species, both univalve and bivalve, in baskets framed so as to admit 

 the water, and at the same time prevent the escape of the crea-, 

 tures, he was enabled to show that his theory was applicable to the 

 whole class. He proved in this manner that the shell was enlarged 

 by the deposition of calcareous matter to the edges of the aperture, 

 and that this deposition was made in successive layers ; that there 

 was no increase from the intusception of calcareous matter, no ad- 

 ditional increase from any action in the shell itself, but that the 

 whole was a successive transudation from certain parts of the living 

 tenant, to which the shell was an inorganic covering. It was ob- 

 jected to him that snails just issued from the egg had as many 

 whorls as the parent, but the falsity of this observation was to 

 Reaumur of easy proof, who found that these young had only one, 



* " De la Formation et de raccroissement des Coquilles des Animanx tant 

 terrestres qu' aquatiques, soit de mer soit de riviere," in Mem. de I'Acad. Roy. 

 des Sc. 1709. 



