DISTRIBUTION OF NON-MEDULLATED NERVE-FIBRES. 29 



It is plain we have here to do with the same cellular struc- 

 tures so often and so well described and represented in the 

 case of the cornea. In regard to a special relation of these 

 cells to the fine nerve -fibres, as was described in the cornea, 

 I have nothing to say. I find, of course, as 1 liave already 

 remarked above, very fine nervous filaments in the tissue of 

 the nictitating membrane, which belong neither to the capil- 

 lary vessels nor to the glands ; fine nervous filaments, which 

 follow a perfectly straight course, are distinguished by regular 

 granular swellings, and have been denoted by us asjliaments 

 of the fourth order. I have never seen any special relation of 

 these to the above cells. 



The opposite appears to be the case Avith the pigment- 

 cells. For we find on the one hand nerve-fibres which cross 

 either the body or a process, or sometimes accompany a process 

 for a short distance, or, finally, we see a nerve-fibre run up 

 to the body or a process, after which it withdraws from fur- 

 ther pursuit. On the other hand, we sometimes see a 

 process of a pigment-cell running out into a filament, the 

 substance of which is sometimes pale, and seem to possess 

 in some cases coarser, in other cases finer swellings ; seen from 

 the surface this appears not quite unlike a nervous filament. 

 We shall return to these structures below. 



If we study the pigment-cells which come into view on 

 gold preparations of the nictitating membrane, we find them 

 singly in its substance or lying together in smaller groups 

 (2-4:) ; they resemble roundish or oblong clusters, which 

 possess in one place or another a short sharp or blunt process, 

 or, on the other hand, exhibit the richly branched processes 

 of various length. For example, if we study a group of 

 pigment-cells as they are represented quite true to nature 

 in fig. 9, with a rather low power (Hartnack 5 or 7), 

 we find they appear as branched structures which, on 

 the one side, appear somewhat sharply broken off"; while 

 towards the other they spread out their arborescent processes 

 as a cephalopode its tentacles. We remark further that the 

 processes do not all break off sharply, but that they are pro- 

 duced further with more or less indistinct outlines, though 

 still there are others which terminate boldly and abruptly. 

 If examined more attentively with a high magnifying power 

 (such as No. 10 immersion), they present the appearance 

 delineated in the figure; one very different from that just 

 described. In the first place, it is noticeable that the distri- 

 bution of the pigment is by no means coincident with the 

 extent of the cell itself. The body of all three cells 

 is strengthened on one side, and in this part is furnished 



