ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 469 



lead, will be found more convenient to insert between the glass slip 

 and its cover than circles of card, which are sometimes recommended. 

 The thin sheet lead from the Chinese tea-chests is very suitable for 

 punching, and as it is not porous like card, it yields no air-bubbles 

 by heat. 



D. Von Schlechtendal has* described a method by which it would 

 appear that all the characters of form and colour (?) may be preserved 

 in Aphides and other insects. The method consists of a rapid death 

 and drying of the insect by means of a current of heated air. The 

 Aphis, previously attached to some suitable support, is suddenly and 

 momentarily subjected to the heat of a spirit or other flame, by which 

 it is immediately killed and caused to retain its natural position. 

 Several examples are then carefully roasted in a current of hot air, 

 such as that passing through an inclined glass tube duly made hot, 

 or dried on a sheet of paper moved over a heated metal plate. 



When dry, the specimens are mounted on card by attachment 

 with gum tragacanth ; or, as Mr. T. W. Douglas suggests, more con- 

 veniently on mica, called ' talc,' in the shops, which, as it is incom- 

 bustible, is well suited for a support both before and after drying. 



This method is vouched for as good by Drs. Giebel, Taschenburg, 

 Mayr, and Eudow. 



I have not tried this roasting process, but it must require some 

 address to prevent the shrivelling of wings in such delicately-formed 

 insects, and to provide against the bursting action of the boiling 

 juices. 



A more complete history of the process than the foregoing was 

 given by Mr. Douglas in 1878. f 



M. Lichtenstein has many times been good enough to forward in 

 letters to me preparations of Aphides which have been secured 

 between two films of mica. The insects, he explains, are immersed 

 in a solution of resin in turpentine, ' a natural amber,' and, when all 

 are in due position, the mica films are placed over apertures in card, 

 and then gummed papers, similarly perforated, are pressed upon them. 

 This arrangement secures all in their places. 



Methods and operations in science, like events in history, repeat 

 themselves. Fifty years ago films of mica were used to cover objects 

 for the Microscope, and before the manufacture of the thin glass now 

 so commonly used, it admirably answered its purpose. Under deep 

 magnifying powers, such as 1/12 in., it will be found even now of 

 great service. The mineral may be split by the lancet into films 

 much thinner than glass can be blown in a flat state. Small un- 

 scratched pieces may be selected which are perfectly transparent, and 

 their cost is quite trifling. 



On account of the high refracting power of Canada balsam, the 

 colours of recently-immersed Aphides show themselves very brightly ; 

 and it sometimes happens that tints, quite lost through irradiation or 

 glance on the surfaces, become distinct by treatment with this resin. 



The bright colours and markings of some species are due to the 



* Entomol. NacLrich., iv. p. 155. 

 t Entomol. Mon. Mag., sv. p. 164. 



