1027 



or more nucleoli, but there are fewer that show signs of division. 



I shall discuss at greater length below some of the literature 

 concerning direct post-embryonic division of nerve-cells. 1 will 

 only mention here that IIodhk/) describes four different types of 

 amitotic division of the ganglion cells in full-grown evertebrates. 

 Paladino states that direct division is a veiy common way for 

 young ganglion-cells in the higher vertebrates to increase. 



In fig. 4r7 T reproduce a group of nerve-cells from a silver- 

 impregnated spinal ganglion in a sixty days old puppy. In it the cells 

 are packed close together into a formation shaped like a string of 

 beads, lying within the same capsule. Between the cells at a few 

 places one can also clearly see bridges of protoplasm, which connect 

 cells that are close to each other. The series of sections of the 

 spinal ganglia from this animal show numerous examples of similar 

 gronps (Muller E.) of cells situated within the same capsule. I have ob- 

 tained the impression, however, that they do not occur in equally great 

 numbers in all the spinal ganglia of the same individual; similar 

 groups of cells have been observed in puppies of six and seventeen 

 days — but they were not so numerous as in the sixty days old 

 animal '^). In the 3,5 years old dog, among five spinal ganglia that 

 were investigated, 1 did not come across more than a few of these groups 

 of cells and in the five years old dog among a still greater amount 

 of material, I did not succeed in finding such a group in more than 

 a single place. It is thus an obvious assumption to regard these 

 groups of cells as formations belonging to the post-embryonic 

 growth of the spinal ganglia — forms produced by the spinal 

 ganglion cells during the post-embryonic increase in their number. 



In spite of the considerable number of works that have been publish- 

 ed on spinal ganglia in the course of years, the information 

 about these groups of cells to be found in this literature is exceed- 

 ingly small. Before 1880, however, they had been observed by a 

 number of investigators and were described most thoroughly by 

 P. Mayer '). After that the subject seems to have been almost forgotten, 

 until in 1889 and 1891 Müi,ler Erik *) gave more thorough and 

 valuable descriptions of similar groups of spinal ganglion cells 

 within the same capsule. Since Mijller's description of these groups 

 of nerve-cells they seem to have been neglected again in recent 



1) RoDHE, Ganglienzellkern and Neuroglia. Ein Kapital iiber Vermehrung and 

 Wachsthum der Ganglienzelle. Arch. f. mikr. Anat. Bd. 47. 

 ') The sixty days old dog was rachitic. 

 8) Mayer, S., Arch. f. Psychiatrie, Bd. G, 1870. 

 *) Muller, E., L c. 



