563.7 1 86 



V. 



The Structure of the Graptolites. 



THE following paper is an attempt to lay before English readers 

 an account of recent additions that have been made, principally 

 by Swedish workers, to our knowledge of graptolite structure. The 

 literature referred to will be found at the end of the article. 



Methods of Preparation. 



To investigate the internal structure of graptolites, different 

 workers have used somewhat different methods of research according 

 to the nature and completeness of the material. 



Tornquist (5 and 11), who had at his disposal pyritised specimens 

 imbedded in slate and preserved in relief, ground a series of sections. 

 For each section he used one specimen, with the advantage that the 

 original of each drawing is preserved. Glimbel, and after him Holm 

 (7 and 16) and myself (13, 14, i8), have worked with chitinous 

 material im^bedded in limestone, or, at least, in more or less calcareous 

 rocks. For us, therefore, it was most practical to dissolve the 

 specimens from the matrix by means of acid. For further examination 

 of the cleaned specimens, Holm, as palaeontologists so often have to 

 do, has utilised the instructive accidental fractures, and has also 

 made little dissections. He has, besides, drawn successive stages 

 of ground specimens still in the matrix, while he has combined both 

 methods by cleaning out ground specimens by suitable processes. 



The following lines give a short account of the method I have 

 used, which is more fully described in my work " Ueber die 

 Graptoliten " (18). 



For dissolving I have, according to the nature of the rock, used 

 hydrochloric, acetic, and hydrofluoric acids. From pure compact 

 limestones, from marly and glauconitic or strongly calciferous marl- 

 slates, I have cleaned out graptolites with fairly strong, raw hydro- 

 chloric acid. Adhering slaty lamellae and glauconite granules are 

 afterwards dissolved in hydrofluoric acid. Acetic acid is only used 

 when there is reason to believe that the specimen under examination 

 is more than usually fragile. 



For cleaning out graptolites from strongly argillaceous marl-slates 

 one cannot use hydrochloric or hydrofluoric acid at once, but the 

 lime has first to be removed by soaking with acetic acid, whereby 

 the matrix keeps its shape, but naturally becomes of looser 



