340 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



three giant fibres, the middle one being the largest. 

 They are still situated dorsally, and lie side by side. 



The structure and function, and the history of our 

 knowledge, of the giant fibres in certain Polychaet 

 worms, especially Halla parthenopeia, has been dealt with 

 in great detail by Ash worth (1908), and it therefore seems 

 unnecessary to refer to the subject in detail here. It may, 

 however, be advisable to include a brief account of the 

 structure of a giant fibre as described by Ashworth, as 

 follows : — 



Each giant fibre consists of a sheath composed of 

 interlacing glia fibres of different diameters and embedded 

 in a finely granular protoplasm. The centre of each fibre 

 is occupied by a bundle of fibrillae, also embedded in a 

 matrix known as the interfibrillar substance. The number 

 of these fibrillae in a fibre differs in different Annelids. 

 The space which is always present between the bundle of 

 fibrillae and the sheath of the fibre is filled with a semi- 

 fluid perifibrillar substance, which is colourless, hyaline 

 and contains very fine granules. 



In my preparations of the nerve cord of Tubifex 

 vivulorum only the sheath of the giant fibres has been 

 clearly marked, the fibrillae and the perifibrillar 

 substance not staining at all well, thus giving the fibres 

 the appearance of empty tubes. This is due to the 

 extreme difficulty which is always experienced in 

 attempting to differentiate clearly the fibrillae of the 

 giant fibres. All ordinary methods of preserving and 

 staining the material, with which I was familiar, were 

 unsuccessful, and as Ashworth' s paper did not come into 

 my hands until this work was ready for publication, I 

 have not yet had an opportunity of testing whether his 

 methods of preserving and staining Halla parthenopeia 

 are equally successful in the case of Tubifex rivulorum. 



