232 PROCEEDINGS OF THE AMERICAN ACADEMY. 



b. Methods employed. 



The present observations upon the fibres of Leydig were made upon 

 sections only. These have been prepared from tissues fixed and stained 

 by several methods. The reagent which proved most satisfactory for 

 both contents and sheath was the picro-osmic-acetic-platinic chloride mix- 

 ture of vom Rath ('95, p. 282), followed by wood vinegar. To obtain 

 good preparations, it was very important to allow the material to remain 

 for a long time in alcohal before embedding. Such preparations were 

 valuable for tracing the courses of the cell-processes entering Leydig's 

 fibres, as the sheath was stained black and therefore stood out promi- 

 nently against the clear gray contents of the fibres and the surrounding 

 nervous tissue. In preparations obtained by this method the course of the 

 cell-processes in entering Leydig's fibre could be traced with low powers 

 of the microscope. Other material, fixed in corrosive sublimate, alcohol, 

 or formol, and stained with ordinary hcematoxylin dyes or with iron 

 hsematoxylin, were used for comparison. 



c. Structure of Leydig's Fibres. 



Leydig's fibres from specimens of both C. producta and A. torquata, 

 killed in the vom Eath mixture, differed considerably in the appearance 

 of both the contents and the sheath from those prepared by other means. 

 In sections of material prepared by the vom Rath method the sheath of 

 the fibre was much more prominent than in those obtained by other 

 methods. It appeared sometimes as a single wall with double contour, 

 but more often gave the appearance of being composed of strands or 

 lamellfE (Plate 2, Figs. 15, 16). It becomes black by this treatment, 

 and is readily distinguishable from the neuroglia, which stains brown, and 

 also from all other parts of the nervous system. In this blackening with 

 osmic acid it shows an agreement with the medullary sheath of the nerve 

 fibres of vertebrates. On the other hand, in sections prepared from 

 alcoholic or sublimate material, the sheath, if it could now be called such, 

 was often inconspicuous, and in places seemed to be lacking entirely. 

 Sometimes after such treatment it gave the appearance of strands or 

 lamellae, but it never exhibited the prominent condition which prepara- 

 tions of the vom Rath material showed. This changed appearance of 

 the sheath I believe to be due to its having been partly dissolved by the 

 alcohol, thus leaving in the sections only a part of the original sheath. 



The contents of the fibre in most of the vom Rath material entirely 

 filled the sheath, but occasionally they were slightly shrunken away from 



