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the fibres and tlieii- tactile knobs closely under the highest power, 

 we get the impression that even there where the knobs lie 

 intracellularlj, the neurotibrillae are still surrounded by a very 

 thin layer of pei-itibrillar substance, taking a different stain from 

 the protoplasm of the cell itself. But of course this layer of 

 perifibrillar substance must be continuous with the surrounding 

 protoplasm. The neurofibrillar network remains entirely independent, 

 but a trophic connection of the perifibrillar substance and the proto- 

 plasm surelj must be present. This seems to us to be beyond doubt, 

 and we may venture to suggest, that only now the varicosities reach 

 their full development, are real tactile discs; as long as they lie be- 

 tween the cells, the varicosities are only parts of the nerve-fibres 

 where the neurofibrillae are getting looser and growing out, but 

 OJily when they pass to the side of the fibres and grow into the 

 cells, they become real tactile neurofibrillar end-nets. The rows of 

 varicosities are merely stages of development of the tactile discs. 



The end-knobs or terminal discs in the upper row of cells of the 

 sensory column, which are already on the point of passing into the 

 horu}^ layer, are for the greater part already lying loose in the 

 cells, the nerve-fibres themselves and the connecting stalks atrophying. 

 So in fig. 5 the four knobs, represented by black spots in the upper 

 row of cells, are entirely separated from the nerve-fibres below, 

 and the same fact is to be seen in the fig. 1 and 3, where a part 

 of the nerve-fibre (the stalk of the end-knob) was still stained. The 

 argument, that this independence of the terminal knobs is due to 

 the connecting stalks not being cut in the section examined, is 

 annihilated by a close study of many sections. Thus we can state 

 with perfect accuracy, that the connecting fibre really does not 

 exist any more (at least, is not stained as the functional fibres are). 



The axial fibre shows the same peculiarities as the rand-fibres, 

 but the tactile nets are larger and more rounded ; the axial fibre 

 too runs between the cells until its end; even there where, in the 

 upper part of the column, the entire cross-section is composed of 

 two cells, the line between these cells runs just through the middle 

 of the transverse plane (cf. Huss) and leaves a small room just in 

 the axis of the column, occupied by the axial fibre (fig. 6). The 

 tactile nets grow out from the fibre now at one side and then 

 at the other, and grow into the cells of the sensory column just 

 as it was described for the rand-fibres. 



So we find the same peculiarities of structure in all the nerve- 

 fibres and their tactile neurofibrillar networks. The same cause seems 

 to us to underlie all these differentiations, which we may describe 



