1041 



cells in tlie ependjma and that in the spinal ganglia from nndiffe- 

 rentiated cells among the capsnlar cells. These cells increase during 

 their dilFerentiation into ganglion cells, among others, partly bj means 

 of mitotic division and as far as I can see from my preparations 

 also partly by means of amitotic division. This post-embryonic 

 increase in the number of the cell-material is greater during the 

 first month of post-embryonic life, but seems to continue afterwards 

 as well. It is only during the first month of the post-embryonal 

 life of the individual that one sees mitoses in these cells, but even 

 during its continued life cell-division seems to occur; it then takes 

 place amitotically. These new ganglion cells that have arisen by 

 mitotic or amitotic division seem to develop into neurones, which 

 not oidy i-eplace older neurones that have been destroyed by 

 degeneration (Paladino), but also help to increase the absolute number 

 of neurones. 



Figures of growth for the axons have been shown morphologically 

 in the dorsal and ventral roots of the lumbar nerves of a 17 days 

 old dog '). These figures of growth have been, among various other 

 shapes, claviform — thus under completely physiological conditions 

 the same shape is found for the figures of growth of the axons as 

 is usually found in experimentally produced regeneration of periphe- 

 ral nerves. 



Addendum.. 



It seems as if the post embryonal increase in the neurones can 

 be etfected by external influences. Thus, for instance, it has api)eared 

 that in growing animals (among others Mus luuscuhis var. 

 alhus) the increase in the numbei- of axons can be intensified 

 by suitably adapted and gradually increased training. If, on the 

 other hand, the training has been made too intense, quite a 

 contrary result is obtained — the number of axons has been found 

 to be relatively less in these animals than in the controlling aninials. 

 During my continued investigations of this problem I have succeeded 

 in showing, in, among other animals, a 3,5 year old dog, numerous 

 transitional stages from indifferent cells — as large as small capsular 

 cells — to fully developed ganglion cells. These different transitional 

 stages have been examined with regai-d to the position, size, off- 

 shoots and neuro-fibrillar structui-e of the cells. These questions will 

 be dealt with more fully in a later and more complete account. 



') This is the oldest animal that 1 have investigated so far with regard to this. 



