SCOTTISH HAIRWORMS I37 



the delicacy of some of the diagnostic characters it is 

 essential that care should be taken with the preservation 

 of specimens. Badly preserved specimens have been found 

 in some cases to be unrecognisable. The most satisfactory 

 method of fixing, in my experience, is suddenly flooding 

 the animal with a solution of corrosive sublimate and acetic 

 acid (in, say, the proportion of lOO parts of a saturated 

 solution of the former to 50 parts of the latter concentrated), 

 but any actively penetrating preserving fluid ought to 

 suffice. The specimens may afterwards be preserved in 

 alcohol. Of the commoner fluids a weak solution of formalin 

 is to be preferred as a fixing medium to alcohol. 



As to examination after the specimen has been properly 

 fixed : the characters associated with the hinder end can 

 generally be observed by means of J-inch and ^-inch objec- 

 tives ; but while the latter can resolve in a general way the 

 skin characters, determination to the full can be obtained only 

 by the use of high combinations of lenses such as a ^V-i^ch 

 oil-immersion objective or dry lens of Zeiss's F series. 

 The magnification in such a case, with a No. 2 ocular, may 

 be put approximately at 600 diameters. The ordinary plan 

 of mounting short lengths of the Hairworm in Canada 

 balsam was found to be unsatisfactory, owing to the density 

 of its structures and colour, and to the lack of contrast 

 between the refractive indices of object and medium. 

 Camerano's method^ was, however, adopted with success. 

 Should the specimen be preserved in alcohol, a quantity of 

 glycerine should be added to this, in order that on removal 

 the specimens may not suddenly dry and shrivel. From 

 the specimen so prepared a thin tangential section of cuticle 

 should be shaved off with a razor, and this section mounted 

 for examination in a mixture of glycerine and alcohol. So 

 the difficulties of density and relative refractive indices may 

 be overcome. 



1 Described in Memone della Reale Accademia delle Sctensedi Torino, 

 ser. 2, torn, .\lvii., 1S97, p. 341. 



42 



