30 



E. THE GRAPTOLITES. 



Reference has been made above to Lap worth's use of 

 graptolites in his stratigraphical work. It was quite impossible 

 for him to regard these organisms as mere tools or ' hall-marks.' 

 He realised that, as once living creatures, they deserve study from 

 the biological point of view, and that they have their own place 

 in the chain of evolution of life on the earth. When collecting, 

 he always had his eyes open for specimens which might throw 

 additional light on their life history and biological position, and 

 for anything which might indicate their mode of life and the 

 conditions which brought about their distribution, evolution, and 

 eventual disappearance. 



His collection became very large, but there was hardly a 

 fossil in it which he could not readily refer to, or of which he 

 could not remember the locality, the horizon, and the circum- 

 stances of its collection, even without reference to its label. 



He not only made himself thoroughly acquainted with the 

 whole literature of the subject, both British and foreign, and 

 focussed and tabulated the exact state of knowledge of the grapto- 

 lites themselves, but he made a close study of the living forms 

 which most nearly approach the graptolites in organisation. 



I. Morphology and Classification. 



Apart from one (4) on the ' Graptolites of the Gala Group/ 1872, 

 the first paper devoted exclusively to this subject is that ' On an 

 Improved Classification of the Rhabdophora,' 1873, in which was 

 outlined a grouping that has proved the starting point for later 

 researches, with minor modifications, has secured world wide 

 acceptance, and has stood the test of new discoveries, both 

 geological and biological. 



The function of the sicula as the primitive germ from which 

 the polypary in all graptoloidea is developed is here discovered for 

 the first time. The nature and position of the bud or buds which 

 give rise to the polypary are studied, and the ' angle of divergence ' 

 (sicular or dorsal angle) of branching in bilateral graptolites worked 

 out in relation to the classification of families and genera. The 

 virgula, the shape of the thecae, and the relation of the latter to the 

 common body are similarly studied. The families, instead of being 

 founded on a single structural peculiarity, are *" constituted by 

 assemblages of species, linked together by a large community of 

 morphological characters, and grouped around typical genera." 



In the case of monoprionidian forms the result is regarded 

 by the Author as satisfactory, and their families are so well circum- 

 scribed that *" the slightest fragment of the branch of a mono- 

 prionidian species can be referred at a glance to its proper family." 



* 6, P . 556. 



