eand: nervous system of lumbricid^. 93 



fernung vom Kerne eiu runder oder ovaler heller Fleck mit einem kleinen, 

 von Methyleublau stark gefarbten Koruchen im Ceutrum zu bemerken 

 war." This is probably, he thinks, the centrosome and sphere described 

 by von Lenhossek. 



Heidenhain und Cohn ('97) find the " Microcentrum " in the cells of 

 most of the tissues of bird embryos. In the cylindrical cells of the neu- 

 ral tube the microcentres lie at the extreme outer ends of the cells. In 

 a surface view of a group of these cells their outlines form a polygonal 

 network, " dessen Maschen die iibrigens nicht regelraassig central gestell- 

 ten Microcentren, je eines in einem Zellenterritorium, einschliessen. . . . 

 Findet man in einem bestimmten Zellenfelde das Microcentrum nicht 

 vor, so ist man haufig in der Lage zu konstatiren, dass in dem zuge- 

 horigen Zellenkbrper eine Theilungsfigur enthalteu ist, dass somit die 

 Centralkorper zum Zwecke der Mitose in die Tiefe der Epithelzelle 

 eingertickt sind " (p. 205). 



Biihler ('98) finds excentric nuclei in cells of the spinal ganglia of 

 Bufo vulgaris. In the cytoplasm chromophilous flakes, which are 

 larger toward the periphery of the cell and smaller toward the centre, 

 are arranged in concentric order about a point lying near the cell centre. 

 Certain fibres also participate in this concentric arrangement. Close to 

 the nucleus and on the side toward the cell centre lie two minute £rran- 

 ules staining deeply in haematoxylin and connected by a dark band. 

 About these as a centre are one or two rows of similar but less con- 

 spicuous granules arranged in arcs of circles. Extremely fine radia- 

 tions pass outward from the central granules ; they intercept in their 

 courses the granules of the concentric arcs and are sometimes capable 

 of being followed quite to the cell periphery. Granules staining in 

 haematoxylin occur at rather regular intervals along the course of a 

 fibril. The concentric arrangement is about the approximate cell centre 

 and not about the granules at the centre of the radiating system. The 

 latter centre lies in the line passing through the centre of the nucleus 

 and the centre of the cell as a whole, — the principal axis, as determined 

 by Heidenhain, — but toward the nucleus end of the cell from the cell 

 centre. The " Microcentrum " described by Heidenhain for leucocytes 

 lay at the cell centre. Biihler says (p. 49) : " Bei mehreren Central- 

 korpern gelang es mir fast immer, eine Verbindung in Gestalt eines 

 dunklen Bandes, die primare Centrodesmose Heidenhain's zu sehen." 

 The system described by Biihler corresponds, therefore, to the "Micro- 

 centrum " and " organische Radien " of Heidenhain. 



The results, then, of the work of von Lenhossek and Biihler upon 



