( 458 ) 



as a getting more and more differentiated and independent of the 

 tactile discs (or varicosities) as we draw nearer to the surface of the 

 sensory column. 



When we see now, that Ihe horny layer above the columns of 

 the organ of Eimer is always thinner than in the adjacent parts of 

 the epidermis (so for example in fig. 1, st. c), as it was the case 

 in all the preparations examined, and when we bear in mind, that 

 these prominences on the surface of the snout of the mole are con- 

 tinually exposed to all sorts of mechanical insults, the question, put 

 at the beginning of this paper, may be answered in the following 

 manner: 



The horny layer above the cells of the column of Eimer being 

 \ery thin and composed of a few layers of cells, and the horny 

 scales being lost very soon by desquamation, there must be a continual 

 moving upwards of the cells of the deeper layers of the column of 

 Eimer, to take the place of the thrown off cells. With these cells 

 the nerve-fibres must grow upwards at the same rate. About in the 

 middle of their course these nerve-fibres begin to form tactile discs. 

 These corpuscles first appear as places in the course of tlie fibres 

 where the neurofibrillar structure is looser; these first varicosities 

 little by little pass out of the course of the fibre and grow into the 

 cells of the column of Eimer, and so become real tactile discs. These 

 tactile discs lying at the side of the , nerve-fibres and remaining 

 attached to them by a short stalk, are a direct argument for the 

 growing upwards of the nerve-fibres together with the cells of the 

 column. Othei-wise the cells would take with them the tactile cor- 

 puscles and sever them from the fibres they belong to or draw out 

 the stalks in an oblique direction. Of this no trace is to be found 

 anywhere. It is very probable, that only when the varicosities grow 

 out to small tactile discs and come to lie intracellularly, they acquire 

 a heightened perceptive faculty. As they are continually travelling 

 upwards to the surface, new varicosities are formed underneath in 

 the course of the same nerve-fibre. As soon as the cells undergo the 

 transformation into horny scales, the tactile discs and their connecting 

 stalks and the nerve-fibres atrophy, the former remaining visible 

 longer than the latter. Only the upper rows of tactile discs, of 

 the form of the networks of fig. 2 and fig. 3, seem to be fully 

 developed. 



They are continually replaced by others, coming from below. The 

 nerve-fibres of the column of Eimer chiefly grow at the base of the 

 column and atrophy at its top. 



Perhaps these views may be extended to other intraepithelial 



