iJ74 PROCEEDINGS OF THE MALACOLOGICAL SOCIETT. 



extent. The blue stain thus obtained can be photograplied by means 

 of screens, but for precision it is not to be compared with that produced 

 by additive dye-stuffs. 



Rapid and thorough oxidation of the chitin, without damage to the 

 radulse, may be obtained by the application of an acidified solution of 

 permanganate of potash. After blackening the unci with this fluid, 

 I decolorize with oxalic acid. It is found that almost any of the 

 ordinary stains will now take effect, but as my object is to produce 

 a transparent staining, so that the outlines of one uncus may be clearly 

 seen behind another, and that there may be no blocking out of light 

 by dense shadows from tlie basal plates, I have provisionally selected 

 dahlia as the best colour for the purpose. This gives good results 

 with chromatic plates and a yellow or green screen, when it is desired 

 to take a pliotograph. 



It is also possible to hydrolyse chitin by prolonged boiling in dilute 

 acid, and this process is more speedily accomplished in the presence 

 of picric acid. The hydrolysed chitin is also amenable to treatment 

 with many stains, notably with acid fuchsin and indigo carmine. But 

 in this method there is the disadvantage that unless the structure is 

 less compact than usual, permeation takes a long time ; and the action 

 begins at the basal plates, causing these to be most emphasized in the 

 resulting stained slides. But if it be desired to have a demonstration 

 of the hollow structure of the unci, upon which the cones are built up 

 by superficially induced thickenings, valuable information may be 

 derived from partially hydrolysed specimens. 



The permanganate method will probably answer all requirements, 

 though any other reagent which has the same effect might be 

 substituted. I do not for a moment suggest that this process must 

 supersede the well-known glycerin jelly method, which has been so 

 industriously applied for many years by workers like Professor 

 Gwatkin. But I claim that it gives a truer picture of the radula in 

 all cases, and that the employment of a stain followed by mounting in 

 Canada balsam is in accordance with the soundest principles of 

 microscopy. 



The accompanying plate represents the radula of Polita sydneyennis, 

 Cox {scharffi, Kennard ; Hyalinia cellar ia, var. compacta, Jeff. ?). The 

 upper division shows the specimen in glycerin jelly, the lower 

 division shows the same specimen after staining and remounting 

 in Canada balsam. 



