LEWIS. — POLYCH^TE ANNELIDS. 233 



the wall. Tlie contents were pale, clear, bluish gray in color, and pre- 

 sented a very delicate structure, which is uniform throughout the fibre. 

 Leydig's fibre consists, therefore, of a single nerve fibre, not of a bundle 

 of fibres. I have not been able to discover by any of the methods used 

 anything in the contents of a fibrillar or striate nature. In a few cases 

 it seemed as if the granules showed for a short distance a linear arrange- 

 ment, but not such a condition as could properly be called fibrillar. In 

 sections prepared by ordinary methods of fixing, these fibres often showed 

 shrinkage ; and such appearance might oftentimes lead to the conclusion 

 which Eisig drew in the case of the Capitellidse, viz. that the fibres 

 showed evidence of degeneration. 



It is clear, then, that the results here given regarding the finer struc- 

 ture of Leydig's fibres in the case of Clymene producta and Axiothea 

 torquata agree in almost all respects with those of Friedlaender. The 

 conclusions of the present paper are : — 



1) Leydig's fibre is a tubular structure, consisting of wall and contents. 

 The wall blackens intensely when treated with osmic acid, agreeing in 

 this respect with the myelin sheath of the nerve fibres in vertebrates. 

 In alcoholic preparations the sheath partially or entirely disappears. 



2) The contents of the tube show an exceedingly fine and delicate 

 structural condition, identical with that of the individual nerve processes 

 of ganglionic cells. In sections prepared by the vom Eath method, they 

 present the appearance shown in Figure 16 (Plate 2). There is not the 

 slightest evidence that Leydig's fibre is composed of a bundle of nerve 

 fibrillte. 



d. Relation to Cells. 



As far as regards the topographical relation of Leydig's fibres to the 

 cells connected with them, these two Maldanidae differ markedly from all 

 other annelids in which these structures have been described. 



In all the accounts which I have read of giant cells and connected 

 giant fibres, the cells have been described as showing a metameric dis- 

 tribution. But in the cases of both C. producta and A. torquata, I find 

 no evidence of a metameric arrangement of the giant cells. In both 

 worms the cells which give rise to the giant fibres are situated without 

 any discoverable regularity or symmetry along the sides of the nerve 

 cord, and in a few instances ventral to it. The number of such cells 

 varies in different segments. The giant cells of the two species corre- 

 spond in position only in so far as there is no regular plan of distribution 

 in either case. In both instances they present a well marked and charac- 



