158 now TO WORK 



are well deserving of the careful attention of the microscopist, and 

 especially in researches upon the changes occurring during the deve- 

 lopment of tissues, facts may be ascertained which cannot be made 

 out by investigations among the higher classes. 



251. Of Preparing the Tissues of Insects for Microscopical 

 Examination. Many of the smaller insects may be mounted entire 

 as dry objects, but the hard external covering of the body and limbs in 

 many members of this class is better displayed if freed from the soft 

 parts and preserved in Canada balsam. Moist tissues may be entirely 

 removed by the action of liquor potassae in which they are perfectly 

 soluble, and the hard textures are at the same time softened by the 

 reagent. After very careful washing in distilled water the entire insect 

 or parts of it, may be dried in the position they are intended to take up 

 permanently. They are then to be moistened with turpentine and 

 mounted in Canada balsam. The chloroform solution, p. 50, of the 

 latter substance may be employed with advantage. For the details 

 of the operation the reader is referred to Mr. Thomas Davies' 

 little book on " The Preparation and Mounting of Microscopic 

 Objects," p. 68. 



The Egg Capsules of insects exhibit very peculiar markings upon 

 their surfaces which vary in every species, and even in those which 

 are closely allied the greatest difference often exists. Insect ova are 

 represesented in pi. XXXVII, fig. 237. The eggs may be examined as 

 opaque objects according to the methods described in p. 21, or very 

 thin vertical and horizontal sections may be made and mounted in 

 fluid or in Canada balsam. Upon one surface of the eggs of many in- 

 sects, and very readily in some of the lepidoptera, an orifice surrounded 

 with beautiful markings may be discerned. This is the micropyle. 



252. Tlie scales and Hairs from many insects and Crustacea are 

 well worthy of attentive examination. The scales from the wings of 

 various butterflies and moths form beautiful objects. They should 

 be examined in a dry state and also mounted in balsam. The student 

 will find that the scales of different parts of the body exhibit great 

 varieties of structure, while those of no two species are exactly 

 alike. 



The markings upon many of these scales are so delicate as to serve 

 for testing the defining powers of the highest and most perfect object- 

 glasses. Some of the most elaborate are obtained from the podura, 

 a little hopping insect, common enough in some localities among old 

 dry wood. In order to catch the podurae, Dr. Carpenter directs that a 

 little oatmeal be placed on black paper and left some hours, when it 

 may be transferred to a large clean basin, out of which the creatures 

 cannot leap. Their scales may be mounted dry, in fluid, or in balsam. 



