228 Botanical Society of Edinburgh. 



centres of the -o. Mollusca and the cerebro-spinal system of the Ver- 

 tebrata, and ;;ccordingly they find there is a strict analogy between 

 them, even to the individual pairs of ganglia of which they re- 

 spectively consist, the general result being that the whole of the 

 ganglia, grouped around the oesophagus in these Mollusca, answers 

 to the encephalon, and a small portion of the enrachidion, of the 

 Vertebrata. 



Organs of the Senses. — The auditory capsules are microscopic, 

 composed of two concentric vesicles, the inner enclosing numerous, 

 oval, nucleated otolithes. The eyes are minute black dots, beneath 

 the skin, attached by a pedicle to a small ganglion. They are 

 made up of a cup of pigment, receiving from behind the nerve, and 

 lodging in front a lens, having in advance of it a cornea, the whole 

 enclosed by a fine capsule. The authors believe they have shovvii 

 the dorsal tentacles to be the olfactory organs. 



The organs of touch are, the general surface of the skin, but 

 more particularly the oral tentacles or veil. Taste is most probably 

 located in the lips and channel of the mouth, the tongue being a 

 prehensile organ, and ill-adapted as the seat of such a function. 



In conclusion, the authors comment on the high organization of 

 the Doridee, and express their belief that the genus, as at present 

 understood, will require to be broken up into several groups. 



BOTANICAL SOCIETY OF EDINBURGH. 



July 8, 1852.— Dr. Seller, President, in the Chair. 



The following papers were read : — 



1 . " On the presence of Fluorine in the stems of Graminese, Equi- 

 setacese, and other Plants, with some observations on the sources 

 from which vegetables derive this element," by George Wilson, M.D. 



The author commenced by stating, that the earliest observer of the 

 presence of fluorine in plants was Will of Giessen, who found traces 

 of it in barley, the straw and grain of which were analysed together. 

 The author reported to the Botanical Society, some four years ago, 

 the results of his earlier researches into the distribution of this ele- 

 ment throughout the vegetable kingdom, which were not very nume- 

 rous or very encouraging. One reason of this was the small extent 

 to which fluorine occurs in plants ; another, and practically as serious 

 a reason, was the difliculty of separating and recognising fluorine when 

 accompanied by siHca. The presence of this body in a plant, besides 

 greatly complicating the investigation, rendered the employment of 

 platina vessels essential, and thus limited the amount of material 

 which could be subjected to examination, besides making it difficult 

 or impossible to observe the progress of an analysis. 



The author then stated, that, in the course of some recent investi- 

 gations into the presence of fluorine in siliceous rocks, he had suc- 

 ceeded in devising a process which was also applicable to plants, and 

 could be carried on in the ordinary glass vessels of the laboratory. 

 The process in the case of plants was as follows :— The plant under 

 examination was burned to ashes as completely as possible. The^ 



