216 [September, 



yellowish bundles of fat irregularly outlined, extending practically the full 

 length and varying in width." Also that the larva lives on cabbage and related 

 plants affected by Aphis brassicx ; and on sycamore affected by Longistigma 

 caryiB. The S. torvus, therefoi'e, of our British lists may prove to be diiferent 

 from Osten Sacken's species. — O. C. Champion, Horsell, Woking : July, 1912. 



Ho}ij to use Schrocder's Prism-eye-piece camera lucida. — Several entomological 

 specialists, including the late Baron E. de Selys-Longchamps and Mr. Verrall, 

 have regretted their inability to use a camera lucida in drawing. The difficulty 

 experienced by them arose partly from improper adjustment of light (the light 

 reaching the eye throi^gh the microscope, and that reflected to it from the 

 drawing paper or card), and partly from the object to be di-awn shifting, through 

 parallax, its apparent position on the paper. Expedients are well known for 

 the regulation of light, such as increasing that thrown upon the object, using 

 diaphragms, or laying paper over the mirror to reduce excess of light coming 

 through the microscope, or shading with ground glass or the hand the surface 

 of the di'awing board : but parallax I'emains. This difficulty, however, can be 

 easily surmounted also. First look inside the Schroeder eye-piece to make siu'e 

 that the prisms completely cover the circular apertiu-e of the eye-cap of the 

 apparatus to be fitted on to the microscope : then, having put it on to the eye- 

 piece, set the lower edge of Schroeder's franu^ parallel with the horizontal edge 

 of some part of the microscope stand ; incline the tube of the microscope until 

 the field of vision in view through the oval external apertiu'e of Schroeder's 

 instrvunent becomes circular and centred upon the drawing-board laid horizon- 

 tally 10 inches below the eye-piece. The centring can be assured by drawing 

 on the board two diameters intersecting one another in the centre at right 

 angles, and marking off upon them points where they are cut by circles drawn 

 from that centre at distances equal to radii of different fields of view previously 

 ascertained, and then making the circumference of the field of view under 

 observation pass through 3 points out of 4 equi-distant from the centre (the 

 fourth mark being commonly out of view). Also have ready a piece of sheet 

 brass, shaped and beaten to fit saddle- wise upon the prism-case of the camera, 

 and capable of being moved forwards or backwards a little vipon it, having at a 

 distance of 5 millimetres from the microscope end a circular perforation 1, or 15 

 millimetre in diameter-, pierced through in the middle of the breadth of its upper 

 side. This fitted over the Ramsden spot (visible with a lens within the oval 

 aperture of Schroeder's eye-piece) preclvides parallax. By shifting the saddle 

 the circular hole in it can be centred upon the spot mentioned, the area and 

 position of which vary with the object-glass and eye-piece of the microscope 

 employed. — A. E. Eaton, Northam, Devon : July, 1912. 



