( 'IS'i ) 



Zoology. — ''Physiological regeneration of neurofibrillar endnets 



(tactile discs) in the organ of Eimer in the mole. Bj Dr. 



J. BoEKE and Dr. G. J. de Gkoot. (Communicated by Prof. 

 G. C. J. Vosmaer). 



(Communicated in the Meeting of November 30, 1907). 



In recent years several authors (Ranvier, von Lenhossek inter alia) 

 have called attention to the fact, that there where intraepithelial 

 nerves in mucous membranes or in the epidermis are found pene- 

 trating even between the superficial layers of epithelium cells covering 

 the sensory surface (so for example in the peribulbar nerve-endings 

 between the taste-buds in the papillae of the tongue, etc.), we have 

 to draw the conclusion, that at the same time as the superticial cells 

 degenerate and are cast off, the sensory nerves with their knob-like 

 end-swellings or end-loops of the neurofibrillae must undergo a 

 perpetual change and growth. But then these are always the fine 

 ramifications and endings of the nerves, which branch between the 

 deeper layers of epithelium cells. Real neurofibrillar endnets like 

 those which are formed round the base of the tactile cells of Merkel, 

 are always found in the deeper laj^ers of the epidermis, where they 

 lie protected by the other epithelium cells. These tactile cells now^here 

 degenerate so quickly as it is the case with the superficial cells 

 of the upper layer of the epithelium, and need not be replaced 

 by other cells coming from the deeper strata. There is no need of 

 a quick regeneration of the neurofibrillar endnets (and the tactile cells). 



But suppose we had a tissue, where in the uppermost strata of a 

 stratified epithelium, in which the superticial cells quickly degenerate 

 and are cast off, we find real tactile cells with distinct neurofibrillar 

 endnets, which therefore must degenerate at the same time as the 

 surrounding cells, how would the process of regeneration of the 

 neurofibrillae take place there? 



In the course of investigations carried on in the histological labo- 

 ratory at Leiden we found a favourable object to study this question 

 in the sensory organs in the snout of the earth-mole (Talpa europaea). 



Here we find an extremely sensitive tissue (the organ of Eimer) 

 the elements of which are only protected by a very thin horny layer, 

 and which by reason of its lying at the tip of the snout must, on 

 account of the well-known habits of the animal, continuously form 

 new jiorny cells for the protecting hornj' layer above, because other- 

 wise the functional cells would very soon come to lie at the surface 

 and be liable to be injured. 



