82 



The Naturalist. 



The oven may be of sheet iron or tin. A round or square tin canister 

 will do very well, provided a hole an inch or inch-and-a-half in diameter 

 be cut in the lid or bottom. The canister should then be laid on its 

 side and heated by means of a spirit lamp or gas jet. The temperature 

 to be employed must be found by experience, but as a rule a dark 

 larva will bear a greater amount of heat than a light or green one. 

 Care must be taken, also, in drying hairy larvse, for if too great a heat 

 be used the hairs will be singed, and the specimen spoiled. In drying 

 the larvse, the blow-pipe should be held horizontally, the operator 

 resting his elbows on the table — and not vertically, with the larva 

 hanging head downwards, as recommended in the paper above- 

 mentioned : for, apart from the disagreeable and injurious effects of 

 the heated air on the eyes of the operator, in nine cases out of ten the 

 larva will have its head burnt before the tail is perfectly dry. Again : 

 supposing the heat employed be not sufficient to burn the larva, the 

 exertion of keeping up a sufficient force of wind is very much greater 

 in a standing than in a sitting position. 



Now for the process. In selecting a larva for preservation, pick 

 one, if possible, soon after changing its skin, as the new skin is both 

 brighter in colour, and not so thick as in an old one, and therefore 

 requires less heat. Kill it by dropping into spirits of wine, or in the 

 cyanide bottle. Personally I prefer the spirit, for it acts much 

 quicker and with more certainty. For hairy larvse, too, it is an 

 advantage to have the skin moist while pressing the larva, as then the 

 hairs are not so liable to be rubbed off. Having killed the larva, 

 empty the skin of its contents by rolling over it, from head to tail, a 

 piece of glass tubing, or round piece of wood, e,g. a lead pencil — taking 

 - care to commence rolling at a short distance from the anal aperture \ 

 for if the whole of the viscera be forced forward at once, there is 

 danger of bursting the skin. Too much pressure should not be used, 

 or the colouring matter will be rubbed off the inside of the skin. In 

 green larvse the colour in great part depends on the food in the 

 intestinal canal, so that no care can entirely prevent the colour from 

 being lost in these larvse. Some recommend the use of alum-water as 

 a peservative of colour, but I have not found any better effects by its 

 use. 



After the skin is emptied of its contents, it should be gently pressed 

 between blotting paper, to absorb any superfluous moisture, and then 

 the blow-pipe should be inserted, the steel spring clasping the larva by 

 the anal flap, as it is termed. Upon blowing through the tube the 

 skin will be distended, the right amount of pressure to be used being 



