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



endothelial cells^^ which apparently arise from the same 

 embryonic tissue from which the longitudinal muscles are 

 developed. The material at our disposal is, however, not 

 young enough to enable us to trace the details of the process. 



11. Nervous System. 



Methods. — Examination of the fresh nerve-cord of 

 Arenicola is not of great use (except for the study of the 

 ''giant-fibres") on account of the pigment and blood- 

 capillaries. We have tried a number of the modern methods 

 for determining the course of the nerve-fibres and the 

 histology of the cellular and fibrous parts of the cord, and 

 the results of these trials are given below. 



Numerous attempts to obtain staining of the elements 

 (particularly the giant-fibres and giant-cells) of the cord 

 by methylene blue were ineffectual. The same process 

 applied to Nereis or Polynoe resulted in a selective 

 staining, which at the present time, fourteen months after 

 the colour was fixed by Bethels ammonium molybdate method, 

 is as sharp as it was when the preparations were first made. 

 But though we tried three species of Arenicola and varied 

 the process in several ways only a very few preparations 

 were at all successful, and in none of these could we trace 

 the origin of the giant-fibres from cells of the cord or brain. 

 Impregnation by Golgi's rapid method was given a trial, 

 but, as other workers have discovered, this method rarely 

 gives satisfactory results with marine objects. Most of our 

 observations are based on sections fixed with the corrosive- 

 acetic mixture and stained with iron-li£ematoxylin, but for 

 comparison with Apathy's (1897) results, we have employed 

 the hsematein stain 1 a of this author (the details of the 

 recipe are given in the treatise 1897, pp. 715-16). For 

 differentiating the giant-fibres and other stout tracts, vom 

 Rath's picro-osmic-acetic mixture was tried, since both Lewis 



1 The appearances presented by this endothelium from diiftrent parts of 

 the coelom have been figured and described in Arenicola marina by 

 Viallanes (' Ann. Sci. Nat.,' ser. 6, vol. xx, 1886). 



