1906.] 129 



FORMALIN A.S A REAGENT IN THE PREPARATION OF SOME 

 SOFT- BODIED COCCID.E. 



BY E. KllNEST GRF.EN, F.E.S. 



Those entomologists vvlio may have had occasion to mount for 

 microscopical study such soft-bodied species of Lecanium as hesperidmn 

 or longulum, must have noticed how difficult it is to bring out the 

 dermal characters satisfactorily in a permanent mount. After treat- 

 ment with the usual boiling potash solution, the skin becomes so thin, 

 clear, and transparent, that the derm - cells and other cuticular 

 characters disappear, and under these conditions the chitin refuses to 

 take up any of the usual stains. I have hitherto found great 

 difficulty in permanently demonstrating the derm-cells in L. viride 

 and Pulvinaria psidii. Though, with careful adjustment of the light, 

 these characters may be visible in temporary preparations (mounted 

 in glycerine), they are again obscured in the final balsam mount. 



1 have recently — and by accident — discovered a means of over- 

 coming this difficulty. Some tubes containing specimens of a 

 Lecaniuin — preserved in three per cent, formalin — were received from 

 the West Indies for determination. They proved to be Lecanium 

 viride, and 1 was agreeably surprised, on mounting these specimens 

 in the usual way, to notice a remarkable improvement in the finished 

 mount. The derm was toughened and retained its form ; it took and 

 held the stain (fuchsin) firmly, the dermal ceils being thrown into bold 

 relief. The marginal hairs also were better defined than in prepara- 

 tions from dried specimens. The earlier stages of preparation are 

 correspondingly facilitated. The maceration in potash results in a 

 more thorough decomposition of the contents of the body, which are 

 consequently more easily removed, leaving the external chitinous 

 parts clear and unobscured. 



The advantages of the formalin treatment are more marked in 

 the ease of the soft-bodied Lecaniince : but many Dactylopiince and 

 Monophlebince are benefited by similar treatment. I have not yet 

 experimented with Diaspidince, which — from their small and sheltered 

 positions — would not lend themselves conveniently to this treatment 

 unless first removed from their covering scales. 



It is necessary that the specimens should be immersed in the 



medium while still fresh. Subsequent immersion of previously dried 



specimens does not produce the same result : nor does the addition of 



"malin to the potash, during the maceration process, have any 



ficial effect. 



