1891.] MICROSCOl'ICAL JOURNAL. 11 



percha four and a half by two and a half inches, soften it in hot water, 

 and bend up its edj^es into a dish. Drop on the bottom of this some 

 of the wax and Canada balsam mixture, and while it is warm and soft 

 stick the back of the insect into it ; in this way we get rid of the pins 

 which, under the old plan, were in the way. When the composition has 

 set and the insect has been securely stuck down, the water and the spirit 

 may be poured into the dish and the dissection commenced. This may 

 be done under either a regular dissecting microscope, or by an ingeni- 

 ous arrangement which mav be constructed in this manner : a stout 

 wire of brass or iron should have one end fastened into a heavy square 

 foot of lead, the other end of the wire must be bent into a ring, which 

 will hold a watchmaker's eye-glass. The trough containing the insect 

 should then be mounted on a block of wood to bring it within the focus 

 of the glass. In carrying out the dissection the eye is placed in contact 

 with the circular frame of the eye-glass, and by raising or lowering the 

 head the focus is adjusted, the weight of the leaden foot keeping it in 

 position, and allowing a movement up or down as the exigencies of the 

 dissection demand. Some operators hold the glass in their orbit as the 

 watchmakers do, but this 'involves much muscular fatigue. A low 

 power objective, such as an inch and a half focus, may also be em- 

 ploved, but the constricted field of view does not compensate for the 

 higher magnification. If the student can afford a binocular erecting 

 microscope, this is the acme of perfection and convenience, and by its 

 means and a steady hand the author has often dissected out the salivary 

 glands of a flea. Having this or any similar arrangement, cut up the 

 brown chitinous skin on each side of the abdomen with the scissors, 

 taking care that their points do not penetrate so deep as to injure the 

 internal organs. Then, with the forceps, raise the skin, beginning at 

 the thoracic end, and as it is raised clear away the tracheal attachments 

 by the aid of needles free from all traces of rust. It is here the gilded 

 needles will be found so advantageous, for these delicate tracheic cling 

 with great tenacity to anv roughness, and although at this stage of the 

 proceedings it would not be of much consequence, at a later period 

 such a catastrophe as the entanglement of the tracheal tubes in a rusty 

 spot would be fatal to success, and spoil the work of hours. 



If the brain and neural system are to be dissected, place the insect 

 in the wax composition on its ventral surface, dissecting from the dor- 

 sum. Any organ which may be deemed worthy of preservation may 

 be detached with scissors, and after staining may be mounted in diluted 

 glycerine. It is advantageous to have a knowledge of the names and 

 uses of the various organs, and a reference to Burmeister and Lowne 

 may furnish information relative to some of these. It is one of the dis- 

 advantages of the present state of entomological science that informa- 

 tion is scattered all through literature instead of being gathered under 

 one compilation. This is in brief the method to be pursued in all 

 insect dissections, enabling the student to compare the variations of the 

 organs in diflerent subjects ; for instance, those peculiar glandular 

 bodies found in various insects, the rectal papilla;. In the blow-fly 

 they are four in number, of a pyramidal shape, projecting from the 

 walls of the rectum, where they perform the functions usually carried 

 on by the kidneys in the higher animals, of secreting uric acid. Well- 

 formed crystals are frequently found in the pouch. The same organs 



