J 039 



then situated most fi-eqiieiitly in tiie neigbourliood of the central 

 canal (fig. 15). If tlie cell is at a somewhat later stage of develop- 

 ment, an incision of the nucleus is usually accompanied bj a division 

 Of the surrounding protoplasm, which even at the same stage shows 

 protoplasmic processes engaged in development (fig. 10). Cells of 

 this last type are situated farther away from the ceuti-a! canal. 



It is noteworthy that the sti'ucture of the Jiucleus in the cell engaged 

 in amitotic division seems to be relatively intact in comparison with 

 the corresponding condition in mitotic cell division. 



With regard to the degree of the neurone formation 1 think that, 

 on the ground of the reasons given above, I may go a step furt[ier 

 than Pat.adino when he writes: "En conclusion, le tissu nerveux 

 lie fait pas exception a la loi, d'après laquelle tout tissu vit dans 

 I'ensemble et se renouvelle isolement, pour lemplacer les elements 

 qu; se détériorent et se détruisent; en d'autres termes, le tissu ner- 

 veux, lui aussi, est nn siège de regeneration pour ainsidire restauratrice." 

 It seems to follow from what has been shown above that we are 

 not dealing with merely a restoration of, but also with iiu increase 

 in the number of neurones. 



In order to complete this survey I shall add the results of my 

 investigations of the 



Appearances of growth 



of the axons in the dorsal and ventral roots of the spinal nerves. As 

 has already been shown above, the calculations of the number of 

 the nerve fibres in cross-sections of the dorsal and ventral roots of 

 the spinal nerves made at a, ajixwdb, 6; text fig. 1 gave such values 

 that one might expect that figures of growth might also really be 

 shown in longitudinal sections of these roots. Silver-impregnated roots 

 from some intact lumbal nerves of a 17 days old dog were set np 

 in series of sections of suitable thickness, and then the preparations 

 were searched for figures of growth. These investigations showed 

 the occurrence of a large number of figures of nerve-fibres free 

 from medullary sheaths, whose ends are situated between the two 

 section surfaces of the preparations; the shape of these ends shows 

 that they could scarcely* be due to the nerve-fibres having been cut 

 off when the sections were cut. Of the different shapes that the 

 ends of these nerve-fibres take I will only mention one here, namely, 

 that which shows a swelling at the point; this swelling has in most 

 cases a claviform shape (figs. 22, 23, 24, 25, and 26). The nerve- 

 fibres in these cases were very fine, and showed repeated convolu- 

 tions during their course (fig. 26). A large number of such nerve- 



