and Laboratory Methods. 'io97 



Mounts of spoiigWa in a relatively large amount of water may often be kept 

 in good condition for two days or more, and hydra in the open top cells live for 

 several days. 



Ihc demonstration of all the siuressive stages in the nietatnorpJwsis of an insect 

 7V!th living specimens. 



This offers an interesting and instructive series of experiments. One of the 

 best species with which to do this is the mosquito. Eggs, larvai, pupae, and 

 imagos are readily obtained during the warm season, and in winter may fre- 

 quently be found in warm greenhouses, where the eggs are laid in barrels of 

 liquid fertilizer after the heat due to the fermentation process has subsided. 

 Egg masses should be mounted for projection in hollow-ground cells. Larvae 

 and pupae may be collected with a tine mesh wire strainer and mounted in clear 

 water in an open top cell. When projected on a screen with low power objec- 

 tive, their peculiar wiggling, the elevation of their caudal spiracles to the surface 

 for the purpose of respiration, the cleaning of this spiracle with the mouth parts 

 when it has become clogged in any way, and the ordinary movements of their 

 mouth parts in feeding are easily demonstrated. To quiet them so that more 

 detailed studies may be made with higher power objectives, add to the water in 

 the cell two or three times its volume of one per cent, solution of chlorotone. 

 At first the larvae become very active, then gradually cease wiggling and only 

 the mouth parts are actively moved, and soon the animals fall to the bottom in 

 a completely passive state. By diluting the anesthetizing solution with water 

 the semi-passive state may be prolonged, and this has been found to be a most 

 favorable condition for the study of the mouth parts. If not subjected to the 

 action of a strong solution of chloretone for too long a time, the larvae may be 

 revived by withdrawing the anesthetic and adding clear water. Adult mosqui- 

 toes may be projected alive when mounted in a life box or glass cell as described 

 below, but they are too delicate to endure the heat from a strong light for any 

 great length of time. For temporary mounts they may be placed in water in 

 hollow-ground cells so as to give dorsal, ventral, or lateral views. 



Open ring cells (Fig. 9, Nos. 18 and 19) are apt to leak water over the top 

 as a result of capillary action ; but it may be stopped by smearing the upper or 

 cut edge of the ring, especially at its points of contact with the slide and cover- 

 glass, with a very small amount of vaselin or paraffin. 



D. Mounting live insects, e. g., flies, mosquitoes, bees, grasshoppers, and 

 crickets, in air in life boxes and glass cells (Fig. 9, Nos. 10 to VI). 



Many of the larger and stronger species of insects are easily held in the 

 hand and placed in the box and quickly covered. Delicate species and those 

 which are apt to sting may be caught in a wide mouthed bottle or under a 

 beaker. To transfer them to the cell place a card over the mouth of the bottle 

 or beaker, with a pen-knife cut a hole in the card a little smaller than the diam- 

 eter of the cell, place the cell or cover of the life box over the hole, and induce 

 the animal to pass through either by shaking or holding toward the light. As 

 soon as the animal has passed into the cell slide it along the card to prevent its 

 returning to the beaker. Next place the cover of the cell, or bottom of the life 



