42 



treating the specimen tor some hours with an extremely dilute solution of Eau de Javelle, 

 with the view of increasing the permeability of the cuticle : - - a method which has been 

 recommended for the preparation of Nematoda : but the reagent in question readily destroys 

 the interna! organs if used too strong, and it is very difHcult to regulate its action in such a 

 way as to obtain a successful result. 



I have tlius been obliged to depend mainly on glycerine-preparations. The specimen is 

 transferred from 70 p.c. alcohol into a solution of glycerine in 70 or 90 p.c. alcohol which is 

 sufhciently dilute to cause no appreciable contraction of the body-wall of the spirit-material. The 

 specimen is then left exposed to the air, in an open watch-glass, for about two days, during 

 which the greater part of the spirit evaporates; and is finally mounted in some of the glycerine 

 which has thus concentrated itself to a strength which is in equilibrium with the air. 



For mounting the slides I have made use of a method which has been elaborated by 

 Mr C. F. Rousselet, to whom I have to express my acknowledgments for information which 

 he has kindly given me. A "cavity-slide", or one in which a depression has been ground, is 

 used for this purpose ; and the first operation is to make an extremely narrow ring of gum- 

 dammar dissolved in benzol, immediately outside the depression in the slide. This process is 

 effected with the aid of a turn-table ; and the benzol evaporates so quickly that the slide is 

 ready for use as soon as the ring has been made. The object of this procedure is to raise the 

 cover-glass (a circular one, the diameter of which is slightly greater than the ring of gum- 

 dammar) above the level of the slide. After placing the specimen, in glycerine, in the cavity of 

 the slide and putting the cover-glass in place, the excess of glycerine is removed as completely 

 as possible by means of a fine pipette or filter-paper. If this operation has been successfullv 

 accomplished a circular space is left between the gum-dammar and the edge of the cover- 

 glass into which the cementing substance can be introduced. The escape of the glycerine 

 is thus prevented by a circular ring of cement between the outer margin of the cover-glass 

 and the slide and forms a more efficiënt closure than in the more usual method of mounting, 

 in which the cement merely passes from the slide over the edge of the cover-glass to its 

 upper surface. 



The cements used have been, following Mr Rousselet's advice; - - first a ring of "picture- 

 copal" varnish, allowed to dry for 24 hours; and after that several successive rings, added at 

 intervals of a day, of a mixture of equal parts of picture-copal varnish and gold-size. For 

 thicker specimens a glass-cell has been used, cemented to an ordinary slide, instead of the 

 cavity-slide. In order to avoid the escape of the cement into the cavity enclosed by the cell, 

 the glass-ring should receive several successive rings of the copal-gold-size mixture, on its lower 

 edge, several days before the cell is required. The attachment of the cell is then readily effected 

 by placing it in position on the slide and hearing it over a flame. Before the glycerine is placed 

 in the cell the upper surface of the glass-cell should receive a ring of the cement which should 

 be left for some hours, long enough to allow it to become partially dry. The cover-glass should 

 be slightly larger than the diameter of the cell, so that a narrow margin, to which the cement 

 can adhere on the under side, is left projecting beyond the cell. Several successive rings of 

 cement are added, as in the case of the cavity-slides. 



