NOTES AND MEMOEANDA. 457 



in It to form a bundle, or in the presence or absence of a 

 Schwann's sheath and a medullary sheath. 



The author believes that the parietal nuclear bodies are 

 secondary formations, from the fact that they are not seen on 

 the finest nerve terminations, and are surrounded with only 

 a small zone of protoplasm. These bodies are held to play 

 a different part in the development of the nerve from that of 

 the corpuscles of the bifurcations, which are an earlier 

 formation. 



Hensen's statement (' Virchow's Archiv,' Bd. xxxi, p. 58) 

 that when the nerves first appear they are exclusively formed 

 of fibrils is denied by Leboucq, for he maintains that at the 

 bifurcations of terminal nerves there is always to be seen a 

 thickened mass, more or less developed, which assumes, in 

 places, the appearnce of a stellate ganglion cell. These are 

 the elements ('^ Nervenbildungszellen") which most authors, 

 since the time of Schwann, have regarded as the starting- 

 point in the development of nerves. Leboucq has not seen 

 any of these cells isolated, as some authors have asserted, but 

 always found them in more or less connection with the 

 nerve-terminations. However, as he has not made many 

 observations in reference to this special point, he does not 

 discuss the origin of these cells further. 



Turning now to the development of the nerves, the author 

 suggests that the embryonic cells found at the points of 

 bifurcation may themselves give rise to the primitive fibrils, 

 just as, according to Max Schultze and Boll, the connective- 

 tissue fibrils are developed from the protoplasm of the con- 

 nective-tissue corpuscles. According to Leboucq, these special 

 cells are, in the first instance, non-nucleated masses of pro- 

 toplasm. The activity of the protoplasm shows itself, on 

 the one hand, in the formation of fibrils ; on the other, 

 in the development of a nucleus. This subsequent ap- 

 pearance of a nucleus in these " Nervenbildungszellen" has 

 been recently described by Calberla (' Archiv f. Mikros. 

 Anat.,' Bd. xv, p. 455). Leboucq cannot state definitely 

 whether the other nuclei which are found on the nerve-fibres 

 (" parietal nuclei") are also derived from the embryonic 

 cells, though he considers it probable. He assigns to these 

 parietal nuclei a separate role in the subsequent development 

 of the medullary sheath. 



Formation of the Medullary Sheath. — Certain bundles of 

 fibrils (axis cylinders), which have been developed in the 

 manner already mentioned, now undergo a peculiar trans- 

 formation, and become invested with a medullary sheath. 

 The period at which this occurs varies widely. But the 



