1815.] On the ^Orthoceralites of Scotland. 199 



alcohol ; but it was never possible to perceive the least lateral 

 ramification. So constant an agreement in researches so delicate 

 seemed sufficient to lead to the conclusion that the dorsal vessel of 

 insects has no ramifications ; but as I had not attempted every thing 

 which it seemed possible to do to ascertain the point, I continued 

 tny researches. 



The acids appearing to me proper to coagulate the humour of the 

 dorsal vessel, I put some drops of nitric acid on this vessel. The 

 contraction of the organ immediately ceased, but the life did not 

 appear injured, and the insect continued to agitate its members as 

 before. The dorsal vessel, and the humour which it contained, 

 became whitish ; and as the alteration gradually extended itself to 

 the muscles, they also became whitish, but with a pearl-coloiued 

 lustre quite peculiar. The dorsal vessel filled vvith a coagulated 

 liquor has thus become more easily observable. On lifting it up 

 with precaution, I did not perceive the smallest fibrilla issuing 

 from it, excepting the tracheye which pass into it. It is always 

 easy to distinguish these organs, because the nitric acid does 

 nothing else than increase their lustre. I afterwards tried the action 

 of various other acids, and always obtained the same results ; only 

 they appear more speedily when sulphuric acid of 69° is used. 

 The action of acids is advantageous to enable us to follow the 

 direction of the muscles, as they communicate to these organs a 

 brilliant pearl colour, and render visible the bundles of which they 

 are composed. 



Injections made with solutions of tannin have always shown me 

 the dorsal vessel without any kind of ramification. The same was 

 the case when the solution was absorbed by the membranes of the 

 y.essel. 



(To be continued.) 



Article VI. 



Observations on tlie Orlhoceratiles of Scotland. 

 By John Fleming, D.D. F.R.S.E. 



(Communicated to the Werncrian Natural History Society, 



May 21, 1814.) 



TriE examination of the history of petrified bodies would be 

 greatly facilitated by the adoption of some regular plan, calculated 

 to give arrangement to the information already obtained, and to fix 

 the attention on those objects which ought to be regarded as of (he 

 greatest im[)ortanee. Thus our knowledge of this branch of science 

 would very rapidly increase, were we to examine with care the charac- 

 ters of the difl'ereiit species, investigate the changes which they have 

 uudcrgf)nr in the mineral regions, and ascertain the various locks in 



