496 F. W. GAMBLE AND J. H. ASHWORTH. 



tubes (sensorisclie Schlauche), partly from their central ter- 

 minations in the neuroglia of the ventral cord of leeches and 

 Lumbricus, and partly from their large size^ non-refractive 

 contents, and myelin and neuroglial sheaths. They are 

 nervous, for they contain the essentially nervous element, the 

 neuro-fibrillge. 



These conclusions are in one way or another at variance 

 with those of almost every other writer on giant-fibres. In 

 Crustacea, for example, the central origin of the fibres in 

 large ganglion-cells of the brain, and their course as deter- 

 mined by Allen, Bethe, Retzius, is entirely opposed to an 

 explanation of them as sensory structures. Neither have 

 they in this group been traced into any connection Avith 

 peripheral nerves except by Apathy himself, and his state- 

 ment is not accompanied by desci-iptions or figures.^ 



In Lumbricus and in an increasingly large number of 

 Polychsetes it has been shown that certain giant-cells of the 

 ventral cord are directly connected with the giant-fibres, 

 and it is usually supposed that each cell gives off a process 

 which fuses with that of the next giant-cell, and so on ; but 

 very rarely do the upholders of this view show that the 

 giant-fibres so formed possess either a connection with the 

 fibrous part of the cord (through delicate fibrillae or colla- 

 teral branches or otherwise) or a connection through spinal 

 nerves with peripheral organs. In the case of Lumbricus, 

 however, it has been shown that branches of the giant- fibre 

 do pass into the nerves (Cerfontaine, 1892). Still, if their 

 origin in giant-cells of the cord can be considered to be 

 proved (and the cases of Sigalion, Clymene, Axiothea, 

 certain Capitellids, and we may add Arenicola, are, we 



* Indications are not wanting in fishes that we must distinguisli two groups 

 of fibres : (1) originating iu the medulla, and traversing the length of the cord 

 without ending peripherally ; and (2) the fibres, such as those described in 

 Lophius, with central spinal origin and peripheral (probably motor) termina- 

 tion. It is possible that the giant-fibres of Crustacea correspond to the 

 first set, those of A.nnelids to the second. The whole question is urgently 

 in need of thorough investigation. 



