114 THE entomologist's RECORD. 



colour of the ova, but there is a large amount of latitude permissible 

 with most of the dry plates on the market. I use the most rapid 

 isochromatic plates I can obtain, always backed to minimise halation, 

 and find that with the 3in. microscopic lens and a magnification of 

 twenty diameters an exposure of two and a half to four minutes, 

 according to the colour of the ova, is about right. With the 5in. 

 Rapid Rectilinear, stop f. 16, magnification ten diameters, and similar 

 illumination, I should give from four to seven minutes, but these 

 exposures might be doubled without detriment to the resulting 

 negative by a slight addition of bromide of potassium to the 

 developing solution. 



For holding ova in position while being photographed I use 

 ordinary glass slips Sin. x lin., such as are used for mounting micro- 

 scopic slides. Ova in situ on bark, portions of leaves, paper, etc., are 

 easily fixed with a small dab of adhesive material, and, where needed, 

 a background of suitably toned paper can be gummed on to the glass 

 slip first, and then the support for the ova fixed upon it. When the 

 ova are loose, and particularly if it be desired to retain them 

 uninjured for subsequent hatching, I find a most suitable method of 

 mounting to be as follows : — Cut out a small square of gummed paper, 

 say fin. each way, and punch out a circular hole in the centre ^in. in 

 diameter. An ordinary cork boring drill does this admirably. Then 

 cut another smaller square of paper, tinted to suit the ova in question, 

 and gummed on one side. This should be a little larger than the 

 hole alluded to above, say j%in. square. Place the small square, 

 gummed side upH-anis, in the centre of the glass slip, moisten the gum 

 of the larger square, and press it down upon the smaller, so that the hole 

 is entirely filled up, and all is held firmly to the glass slip. Now 

 moisten a fine hair pencil between the lips and pick up a single ovum 

 on the point of it. Breathe upon the prepared gum surface within the 

 Jin. hole, and place the ovum lightly upon it. Continue the process 

 with as many ova as you wish to photograph at once, and they will all 

 be found to adhere quite as firmly as is necessary for the purpose in 

 hand, while they can easily be brushed oft" afterwards, and will be 

 none the worse for the treatment they have undergone. At least one 

 ovum of each species should be mounted upon its side, as it will then 

 be available afterwards to aftbrd measurements otherwise unobtainable 

 from the resulting photograph. 



It is a very good plan to line the box, in which living $ s are put 

 for the purpose of obtaining ova, with paper, as then the ova will be 

 laid in most cases on the paper, and are easily accessible, whereas, if 

 they are laid directly on the sides of the box, these must either be cut 

 up or a thin shave taken from them to obtain the ova uninjured. 



The very worst material I know for photographic purposes on 

 which ova can be laid is cotton wool. Each individual ovum must be 

 separated from every strand of the wool before it can be mounted 

 with any hope of getting it to lie flat, or of placing the entire batch as 

 nearly as possible in one plane (a most important point to remember, 

 or your photograph cannot be in focus all over), while every strand of 

 the cotton which does get mounted with the ova, and there are sure to 

 be some, comes out like a piece of rope, and quite spoils the picture. 

 It is only necessary to try to manipulate ova so laid once, and you will 

 thereafter be very careful to ask all your friends, when sending you 



