108 . ' [May, 



evaporated on a blackened surface. The bottom of the drawers or boxes 

 may be saturated with the solution, the alcohol soon evaporates, but 

 the arsenic remains for practically all time, not being volatile as is the 

 case with most other preservatives. I use the solution principally for 

 touching the bodies of dragon-flies and other large insects w^hen on 

 the setting boards ; insects so touched remain perfectly safe, and it is 

 only rarely that a slight deposit is observable when the solution has 

 been allowed to spread on the wings (not to be compared in any way 

 with that left by corrosive sublimate) ; still this might render its use 

 objectionable in the case of brilliantly metallic or polished beetles, &c. 

 In boxes jjlaced on end a small collection of debris usually accumulates 

 in the lower corners in the course of years, quite independently of the 

 presence of pests ; but these accumulations invite pests, and it is well 

 to drop a small quantity of the solution in the corners. For the 

 " purgatorium " used by those who have time and assistance for 

 " disinfecting " insects before placing them in the collection, it is 

 probable that bisulphide of carbon is to be preferred, as a preliminary, 

 but its evil odour renders it unsuitable for general use. 



So much, then, in favour of arsenic, a preservative that is seldom 

 if ever mentioned so far as collections of insects are concerned. I 

 would anticipate a possible objection by saying that the extremely small 

 quantity held in solution and afterwards deposited is scarcely likely 

 to be injurious to health, and, in fact, the quantity is infinitesimal 

 as compared with that present in collections of bird and other 

 skins. I can state from experience that a small supply goes a very 

 long way. 



The rough draft of these remarks was written several months 

 ago (just after the appearance of Prof. Eiley's book) and forgotten : 

 recent queries as to preservatives have caused it to be sought out, 

 revised, and published. 



Lewisham, London : April, 1893. 



THE DISTINCTIVE AND SEXUAL CHAEACTERS OF CHRYSOPA 

 FLAVA, SCOPOLI, and CE. VITTATA, WESMAEL (Second Notice). 



BY EOBBRT McLACHLAN, F.R.S., &c. 



Under the above heading 1 published a short article in this 

 Magazine, Vol. xx, pp. 161 — 163 (December, 1883). In the course 

 of that article mention is made of its having taken its origin from an 

 examination of some striking examples of " Qh. ■fiava''^ from Central 

 Italy. So far as the form and structure of the wings in Ch. fiava are 



