350 



ORGANIC GROWTH 



SEC. 



and not the cell-plasma is the essential part of a nerve-cell : 

 the latter serves only for conduction. Hence the extra- 

 ordinarv niac^nitude of the nuclei in the Q,anf;jlion-cells of all 

 animals which possess a somewliat highly developed nervous 

 system.^ 



Secondly, this supposition is strongly supported by the 

 peculiarities of the nuclei in the nerve-fibres of the lower 

 multicellular animals. In these fibres, as I liave shown for 

 instance in Beroii, the nuclei, surrounded with very little pro- 

 toplasm, are placed at intervals in such a way that a nervous 

 fibril passing through the nucleolus connects one nucleus to 

 another. Thus these primitive nerves look like chains of 

 nuclei connected by conducting fibrils, and resemble a series 

 of telegraph stations connected together for the purpose of 

 renewing or strengthening the current at the beginning of 

 each stage. Obviously the ganglionic swellings along the 

 nerves in higher animals, e.g. the spinal ganglia, form a simi- 

 lar apparatus, but with the added function of crossing the 

 conducting fibres.^ 



Thirdly, I find that also in the sensory-cells of Medusae 

 nerve-fibrils pass through the nucleolus, and are continued, 

 as already mentioned, into the cilia, or terminate in the nuclei 

 of the epidermic-cells.^ The same thing occurs in the sensory- 

 cells of higher animals. 



Fourthly, nerves frequently terminate in the nuclei of 

 cells which are not sensory, and this mode of termination 

 will, I believe, be found in future to be very common. It 

 occurs, for instance, in the epidermis, in muscle-cells, etc., 

 and in all probability, as before mentioned, in ciliated cells. 



^ Even in the nen'e-cells of Medusae (Carmarina hastata) the cell-plasm 

 obviously consists of conducting fibrils {Medusen, Taf. viii. figs. 8, 10) ; and 

 the same thing is easy to observe in the nerve-cells of the cerebral ganglia of 

 Helix pomatia. 



- Cf. Beroe, Taf. viii. fig. 72; Medusen, Taf. xi. fig. 9. 



^ Medusen, Taf. iv. figs. 1, 7, 21; Taf. xiii. fig. 9, etc. 



