94 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



the same material, the spiual-ganglion cells of the frog, are at consid- 

 erable variance. They agree in showing a concentric structure in the 

 cell body, but von Lenhossek finds the centrosome at the centre of the 

 concentric structure, while Biihler finds his " Centralkorper " near the 

 nucleus and remote from the centre of the concentric arrangement. 

 Von Lenhossek's centrosome is composed of a large number of granules ; 

 Biihler finds generally only two granules composing his " Centralkorper." 

 In the toad and other vertebrates, including mammals, Biihler finds radi- 

 ations from the " Centralkorper ; " von Lenhossek described no radial 

 structures. Biihler, in the paper referred to ( '98), compares critically 

 his results with those of von Lenhossek and other authors. 



Biihler states that structures similar to those described by him ('95) in 

 the brain of the lizard he has seen also in some of von Kolliker's Weigert 

 preparations of pyramid cells from the human brain, and likewise in 

 Cohn's preparations of nerve cells from an adult mouse. 



Hunter ('98) noticed that van Beneden et Julin ('84), in a work on 

 the central nervous system of ascidians, represented excentric invagi- 

 nated nuclei in the nerve cells of Molgula. He consequently was led to 

 investigate the cells of the central nervous system of Cynthia partita, 

 and found the nuclei always excentric and generally at the end of the 

 cell opposite the process. The form of the nuclei varied from spherical to 

 cup-shaped. Occupying the centre of the cell was a structure which he 

 considered homologous to the centrosome and sphere of von Lenhossek. 

 At the centre of a " clearly staining area, homogeneous or finely granu- 

 lar," were one or several *' black deep-staining granules, the centro- 

 some or central bodies of authors.'' Surrounding the clear area was a 

 coarsely granular zone of varying diameter. In some cells were " well 

 developed astral rays, presenting the appearance found in leucocytes." 



There were many modifications of the structure. In some cells all 

 the parts mentioned were found, while in others only a central deeply 

 staining granule was found with no definite cytoplasmic arrangement 

 about it. In very young animals killed shortly after metamorphosis a 

 larger proportion of cells showed the structure than in the adults. In 

 these young cells the sphere and radiations were generally lacking, or at 

 most only a very narrow clear area with a slight condensation about it 

 was found. There were generally two central granules. In the cells of the 

 young Cynthia the nuclei were excentric but rarely invaginated, and the 

 centrosomes seemed to have no fixed position in the cell body, often being 

 found " laterally between the nucleus and the cell membrane." Speak- 

 ing of the absence of sphere and radiations in the young cells, ami the 



