RAND.: NERVOUS SYSTEM OF LUiMBRICID^. 99 



achromatic " Centrodesmose," which he believes gives rise to the spindle. 

 The microcentre is the point of insertion of a system of radiating fibres, 

 which extend to the periphery of the cell. These fibres, according to 

 Heidenhain, are contractile and in a state of tension, which is a source 

 of energy displayed in the mitotic processes. The microcentre lies at the 

 centre of an astrosphere, which is bounded by a layer of microsomes 

 occurring on the radial fibres at equal distances from the centre. The 

 astrosphere is not an organ of the cell, but only a region which takes a 

 characteristic stain because of the concentration of the radial fibres. 



In the giant cells of bone-marrow, which have polymorphic nuclei, 

 mitosis occurs without a division of the cell body. In these cells sev- 

 eral groups of " Centralkorper " were found, each group containing many 

 granules. 



Heidenhain predicted that the microcentre with its radiating system 

 would be found in most resting cells. 



Reinke ('94) found the centrosome and sphere in leucocytes of the 

 salamander. Leucocytes of amoeboid form diftered from those of 

 resting form in having coarser radiations of unequal thickness and 

 thickenings of the fibres arranged in arcs concentric about the 

 centrosome. 



Dehler ('95*) described a microcentre (Heidenhain), without radia- 

 tions, in the red blood corpuscles of the chick embryo. He believed the 

 microcentres to be derived from the centrosotnes of mitosis. 



Driiner ('95) observed centrosomes in the resting sperm cells of the 

 salamander and in resting cells of the gastrula of Triton alpestris. He 

 gives an extended criticism of Heidenhain's mechanical theory of the 

 centred system and sets forth an opposed theory. Driiner believes that 

 the radiations of the resting cell disappear before a mitosis and that new 

 radiations arise from the centrosomes. He divides the mitotic process 

 into two periods, the first ending with the division of the chi'omosomes 

 in the equatorial plate. ^' Die erste Periode ist die der Expansion, die 

 zweite die der Kontraction des gesammten Strahlensystems " (p. 333). 



Niessing ('95) found the centrosome with sphere and radiations in the 

 liver and spleen cells of the salamander and in the liver of the human 

 embryo. 



Vom Eath ('95") described a centrosome and sphere in the large 

 gland cells of the head of Anilocra mediterranea ; also in the hepato- 

 pancreas cells of Porcellio scaber and in spleen cells of a young dog. 

 In amitotically dividing leucocytes and sperm cells there are some- 

 times one and sometimes two centrosomes and spheres. Vom Eath 



VOL. XXXVII. — NO. 3 2 



