THE NERVOUS SYSTEM 299 



suggested that afferent impulses ascend the fine fibrils, pass from 

 the finer to the coarser net, and take their exit by the thick 

 fibril, which can be traced into a motor nerve. Such a transit 

 could not, so far as one can imagine, have any effect upon the 

 distribution of the impulses which pass through the neurone ; 

 besides, there are reasons for believing that the course taken by 

 impulses which are delivered to the ganglion by sensory nerves 

 is determined by the felt work in its centre, the neuropil. It is 

 probable that during their passage through the cell-body im- 

 pulses acquire the energy requisite to discharge the muscles 

 to which the motor-fibre carries them. In vertebrate animals, 

 sensory nerves are branches of neurones of which the cell-bodies 

 lie in cranial or spinal ganglia. They resemble the ganglion-cells 

 of the leech in as much as they are unipolar ; both branches, 

 the one which collects impulses from sense-organs, and the one 

 which distributes them to the spinal cord, come off from the cell 

 in a common trunk which afterwards divides, although the 

 unipolar condition of the cell of the spinal ganglion is not 

 primitive, but acquired. In the earliest stages of its growth 

 the cell is bipolar. Its two ends subsequently grow together for 

 a certain distance, the common portion being the vertical limb 

 of the T (cf. Fig. 21, which shows the growth of a granule of 

 the cerebellum). The body of the cell contains a network not 

 unlike the network of the leech. It is probably related to what 

 may be termed the charge of the neurone, the development of a 

 suitable degree of force in the impulses which pass through it. 

 The neuro-fibrillse of a large nerve-cell, such as a motor cell of 

 the spinal cord, are exceedingly slender (Fig. 22). They branch 

 and reunite. A certain number gather towards the axon ; 

 but the majority pass through the cell from one dendrite to 

 another, or from one branch of a dendrite to another branch. 

 It is very tempting to suppose that neuro-fibrillse are con- 

 nected with conduction. When first discovered they were 

 regarded as conducting strands ; but it is evident that they are 

 not comparable with telephone wires or other isolated or 

 separate conductors. There are good reasons for regarding 

 dendrites as collecting processes, taking up impulses from the 

 end-twigs of the nerves which branch in the grey matter 

 around them, passing them through the cell-body into the 

 axon. The continuation of neuro-fibrillae from dendrite to 



