Herrick, The Development of Nerve-Fibres. 15 



mander larva, where some of the nuclei are actually emerging. 

 Fig. 1 1 , shows the relations as seen in a horizontal section of 

 the thoracic cord near its ventral surface, a — a indicates the 

 position of the median line. The karyokinetic figures near the 

 periphery belong to the sheath, but the others are undoubtedly 

 elements of the root system. At an adjacent level very numer- 

 ous neuroblasts in mitosis are seen near the central canal. 



2. After issuing from the neuraxis the cell masses contin- 

 ue to multiply. Fig. 2 illustrates subdivision of a neuron in the 

 seventh nerve of a very young embryo of Eutaenia near its exit 

 from the medulla. Fig. 10 is an illustration of mitosis in the 

 midst of a fibre of spinal nerve in the salamander larva some 

 distance from, the ganglion. Only a few of the neurons are 

 drawn, but lines mark the width of the nerve. Fig. 12 indi- 

 cates the subdivision of neurons in the ganglion of the eighth 

 nerve, (here only a few cells are drawn.) 



3. The nuclei thus formed are at first continuous with the 

 embryonic fibres out of which the axis-cylinder is formed. 

 Figs. 4, 7 and 8 are introduced to verify this point and were 

 drawn by aid of an excellent one-twelfth immersion and Abbe 

 illuminating apparatus. The preparations are from salamander 

 larvre fixed with chromacetic and platinic chlorid and stained 

 with haematoxylin and acid fuchsin after sectioning in paraffin 

 and walrath in continuous bands. Fig. 5 is a cross section of a 

 similar nerve showing the only case observed where the fibre 

 lay beside the nucleus (a) instead of continuous with it. In all 

 other cases at this stage the nucleus alone occupied the walls. 

 Fig. 6, which cuts obliquely through a spinal ganglion, illus- 

 trates the same fact. Fig. 10 shows that the cells ot a spinal 

 ganglion actually are converted into nuclei, b being regarded as 

 an intermediate state. 



4. In none of the cases cited is there any other source 

 visible for the nuclei, which are obviously rapidly multiplying, 

 than that indicated. There is no evidence of the intrusion of 

 connective elements to associate themselves with the nervous 

 fibres. This is especially true in the salamander, where there 

 is the most diagramatic simplicity in structure. Fig. 9 gives an 



