ANATOMY AND CLASSIFICATION OP THE ARENIOOLID^. 493 



hand^ while many equally competent observers by the use of 

 other methods have shown that even in the earthworm the 

 giant-fibres do arise from an anterior and a posterior group of 

 cells, and that in many Polychsetes they arise from a couple 

 or more, of symmetrically or irregularly arranged giant-cells, 

 yet these observers do not adequately prove a fusion of 

 elements — which on the face of it would be a serious 

 blow to the neuron theory, — and they do not show that 

 the giant-fibres have either fibrillar connections or a mode 

 of termination comparable with that of fibres which arise 

 from cells within the cord. The evidence of their nervous 

 nature is not felt to be so convincing, nor demonstrated by 

 such experiments — for example, on their degeneration and 

 subsequent repair, accompanied by loss and renewal of the 

 power of co-ordination, — as to obtain the general acceptance 

 of anatomists. 



The experimental evidence is undoubtedly very weak. 

 Friedlander (1895), as is well known, has studied the re- 

 generation of the giant-fibres which follows section of the 

 cord in the earthworm. He found that the fibres degenerated 

 like normal nerve-fibres, but that subsequently from each 

 cell a number of new fibres arose in the new part of the cord, 

 but this is almost the only work in this direction. 



The Wallerian or degeneration method has not hitherto 

 been employed, but it will no doubt throw much light both 

 on the course and termination of the fibres, and also on their 

 behaviour under this method as compared with ordinary 

 nerve-fibres. We are, therefore, thrown back upon the 

 anatomical results obtained by the use of various histological 

 tests. By this means it has been shown, for example, that in 

 Lophius, by G. Fritsch (1886), in certain Crustacea (Retzius 

 [1890], Allen [1894], Bethe), and in many Annelids 

 (Spengel [1882], Eisig [1887],Rohde [1887], Lewis [1898], 

 etc.), the giant-fibres arise from giant-cells. In Lophius 

 the origin and course of the fibres was determined in 1886, 

 and their structure has since been examined in detail bj 

 Apathy, but their termination is still unknown. The fibres 



