APPENDIX. 101 



to study the structure of this curious organ with advan- 



tage 



Spiracles (plate 7, figures 212, 213). — These do not re- 

 quire much dissection. They are generally found on each 

 side of the abdomen, almost every segment of which possesses 

 a pair. Excellent specimens are furnished by the dytiscus, 

 bee, blowfly, cockchafer, and silkworm. To prepare them, 

 separate from the thorax the abdominal portion of the 

 insect, and slit it down the centre with the fine-pointed 

 scissors, draw out the viscera, &c., with the curved needles. 

 The air-tubes adhering to the spiracles may be detached by 

 cutting them away with the scissors. Thoroughly cleanse 

 the horny cuticle by repeated washings, spread it out flat 

 between two slips of glass ; when dry, immerse it in spirits 

 of wine or turpentine for a few days, and mount it in balsam. 

 In this manner the whole of the spiracles of an insect, run- 

 ning down each side of the abdomen, will be displayed. 



Trachea (plate 8, figure 222). — The best method we are 

 acquainted with for obtaining the air-tubes of insects is that 

 recommended by Professor Quekett : — 



"By far the most simple method of procuring a perfect 

 system of tracheal tubes from the larva of an insect, is to 

 make a small opening in its body, and then to place it in 

 strong acetic acid : this will soften or decompose all the 

 viscera, and the tracheae may then be well washed with the 

 syringe, and removed from the body with the greatest facility, 

 by cutting away the connections of the main tubes with the 

 spiracles by means of the fine-pointed, scissors. In order to 

 get them upon the slide, this must be put into the fluid and 

 the tracheae floated upon it, after which they may be laid 

 out in their proper position, then dried, and mounted in 

 balsam," 



The best specimens are found in the larva of the dytiscus 

 and cockchafer, and in the blowfly, goat-moth, silkwoi'in, and 

 bouse-cricket. 



Gizzards (plate 8, figures 220, a, h ; 221, a, 6).— Most of 

 the insects from which these organs are procured being of 

 large size, it will be necessary to secure them to one of the 

 loaded corks by small pins. The dissection should be made 

 in one of the shallow troughs, filled with weak spirits and 

 water. Cut the insect open ; the stomach will float out 

 with the gizzard attached to it, in the shape of a small 

 bulbous expansion of the size of a pea. Insert the fine 

 point of the scissors, and cut it open ; the interior will be 

 found full of food in process of trituration. Empty the 

 contents of the gizzard, and wash it out welj; place it for 



