953 



the fact that the numbers for these animals were based on speci- 

 mens on a few investigations. The difference between the number 

 of nerve fibres in tlie dorsal and ventral roots is comparatively 

 greater in old than in 3'onng animals of tiie same species. I shall 

 leave a more detailed discussion of the values obtained for a future 

 and moi'e complete account of the questions that are coniiected with 

 this problem and shall pass on instead to an attempt to answer the 

 following question : 



H01Ü does a post-embryonal increase in the nmnher of axons in the 

 dorsal and ventral roots of the spinal nerves arise f 



This question forces itself upon our attention when we find that 

 the number of nerve fibres in the dorsal and ventral roots of the 

 spinal nerves increases considerably with the growth of the animal. 

 There may, however, be different opinions as to the manner in which 

 this increase takes place, and this question certainly needs to be 

 subjected to a comprehensive investigation. There are really two 

 possibilities to be taken into consideration. The increase must depend 

 either on a T- or Y-formed division of nerve fibres, or on an ontgrotvth 

 from the centre, from nerve cells (neuroblasts) that have been nendy 

 formed or are lyiny in reserve. There is, of course, a third possibility 

 which is, however, not very probable, namely, that one nerve-cell 

 has discharged tivo axons in the same direction. 



Does a division of the nerve fibres exist in the I'oots of the spitial 

 nerves ? 



Most obvious is of course the supposition that we have here a 

 cleavage {T- or F-divisionj of the nerve fibres on the lines of the 

 process, of which such fine examples may be seen in the peripheral 

 part of the nerves and also in the central nerve system. A cleavage 

 of this kind may be exceedingly frequent; thus, at Prof. Boeke's in 

 Leyden I saw a preparation which showed, among other things. 

 a nerve fibre that was divided at one place into six branches. 

 Stefanelli ') describes and reproduces a preparation from the tongue 

 of the chameleon, in which a single nerve fibre was divided into 

 branches terminating in no less than thirty-fi\ e motory plates. Duiing 

 nerve regeneration after a section one may also see abundant 

 examples of such division. See, for instance, the figures in Cajal') 



1) Stefanelli, a. La piastra motrice secondo le vecchie e le nuove vedute. 

 Annali di Neurologia Fasc. IV 1912. Quoted by Boeke L. c. 3. 



') Gajal, Ramon Y. Studiën über Nervenregeneralion (J. A. Barth, Leipzig) 1908. 



