78 THE MICROSCOPE. May., 



with the slide ; by always slipping the mica in the same way, 

 the same color will be obtained, as the color varies with the 

 thickness. Quite a variety of beautiful color effects will be se- 

 cured by either ushig mica plates of varying thickness or by 

 merely using two or more layers of thin plates superimposed. 



The colors will be varied still more by altering the relative 

 position of these plates. Three plates of varying thickness will 

 be all that are necessary to keep. If the first piece of mica se- 

 lected does not suit throw it away and try another. 



In Dallinger's Carpenter (seventh edition,) page 271 itis-^aid: 

 The variety of tints given by a selenite film under polarized 

 light is so greatly increased by the interposition of a rotating 

 film of mica that two selenites, red and blue, with a mica film 

 are found to give the entire series of colors obtainable from any 

 number of selenite films, either separately or in combination 

 with each other. 



Scales of Lepidoptera.— These may be exhibited in their 

 natural arrangement by mounting a small piece of wing dry. 

 If desired as test objects, a slide or thin cover, after having been 

 breathed upon, may be slightly pressed on the wing or body of 

 the insect. 



Some scales as the podurse, show a beaded appearance under 

 high powers from corrugation. With a good wide-angled ob- 

 jective, these appearances may be resolved into exclamation 

 points. 



Stings and Ovipositors. — These objects present a great 

 variety, of structure and are best mounted in balsam. To ob- 

 tain them, press upon the back of the insect until the organ is 

 extended and while extended, sever close to the body with a 

 sharp dissecting knife. They should then be transferred to oil 

 of cloves for a short time, then to turpentine, and finally 

 mounted in balsam. 



Before mounting, it is best to examine them under a dissect- 

 ing microscope and if not properly spread out, to spread them 

 out well with needles. 



Fixing Arranged Objects to a Slide. — A thin solution of 

 clear glue dissolved in alcohol and spread upon a slide, is use- 

 ful for this purpose. As each object is placed upon the slide, 



