Appendix D: Preparation of Microscopical Material 225 



5 parts of water. The same treatment is useful for the larvae of 

 insects. Some such as the nymph of the dragon-fly, will require 

 more chloretone. 



For Various Dissections and Parts of Insects see chap, x, ii. 



For Mounting Insects Entire (beetles, mosquitoes, gnats, aphids, 

 larvae, etc. ) as microscopic preparations, and for mounting muscle, 

 wings, heads, legs, scales, antennae, etc., see chap. xiii. 



Live nymphs of the dragon-fly are especially valuable for study 

 under the compound microscope because they show very clearly 

 the valvular action of the heart, the tracheal gills and tracheae, 

 and the brain and its relation to the eyes. The heart is located 

 well toward the posterior end of the abdomen between the main 

 tracheal trunks. Cole (Journal of Applied Microscopy, Vol. 

 VI, p. 2274) recommends that the animals be anaesthetized by 

 subjecting them to a 1 per cent, aqueous solution of chloretone. 



MOLLUSKS 



Gills of the Fresh-Water Mussel may be fixed in corrosive sub- 

 limate (reagent 13, Appendix B) for from 20 to 30 minutes, 

 washed out in water and then in dilute alcohol to which tincture 

 of iodine has been added. Make cross-sections in paraffin, stain 

 in dilute hematoxylin (reagent 49) and mount in the ordinary way. 



Cross-Sections of the Entire Mussel are valuable to show the 

 relations of the gills, kidneys, and heart. Wedge the valves apart 

 slightly and immerse the animal for 24 hours in 1 per cent, 

 chromic acid (reagent 10). Wash out thoroughly in running 

 water and transfer the specimens to 70 per cent, alcohol for two 

 or three days or until needed. To section, remove both valves, 

 place the animal on a board and with a razor cut transverse sec- 

 tions. These are to be examined with the naked eye or with a 

 dissecting lens. 



To Kill Snails in an Expanded Condition put them into a vessel 

 of cold water, then run a layer of hot water onto the surface of 

 the cold water. See that the vessel is full of water and cover it 

 with a glass plate to exclude the air. 



For Lingual Ribbon of the Snail see chap, xiii, memorandum 7. 



