44 2 Phylum Arthropoda 



cultures so often. Molds are often worse at temperatures below 25°, 

 but may usually be controlled (see below). 



When the adults emerge they may be anesthetized with ether for 

 examination. If the etherization is done with reasonable care it does 

 not damage the flies in any way; neither their length of life nor their 

 fertility is reduced. I use a wide-mouthed specimen bottle, the mouth 

 of which will just fit inside the collar of the milk bottle, in the space in- 

 tended for the pasteboard top. The culture bottle is turned with its 

 mouth away from the light, and tapped until the plug may be removed 

 without flies coming out. The etherizing bottle is then applied to the 

 mouth; the two may easily be held in one hand. They are reversed, and 

 tapping the culture bottle disturbs the flies, which then react positively 

 to the light. The process may be hastened by holding the pair of bottles 

 at an angle, so that shaking makes the flies drop into the etherizing 

 bottle. Into the etherizing bottle is now inserted a cork, to which is 

 wired a piece of cotton that is moistened with ether. The flies are 

 watched until they no longer move, and are then emptied out for ex- 

 amination. They should remain anesthetized for several minutes. The 

 first sign of an over dose is that the wings are held erect, over the thorax; 

 such flies may recover, but in general they should be removed before 

 this reaction occurs. 



Bridges (1932) has described a more elaborate etherizing bottle which 

 is preferred by many workers. It consists of a metal funnel, of a size 

 to fit the culture bottle, cemented to a glass chamber, with a corked 

 opening opposite the end of the funnel, through which the flies are re- 

 moved. There is a collar, filled with asbestos, and having a separate 

 corked opening; the asbestos is saturated with ether. This bottle has 

 the advantages that it anesthetizes more quickly than the simpler one, 

 and that it uses less ether and lets less escape into the room to be ab- 

 sorbed by the experimenter. It has the disadvantage that is is largely 

 opaque, and prevents taking advantage of the phototropism of the flies in 

 emptying culture bottles. Those who use it depend wholly on shaking 

 the flies out by gravity, usually pounding the bottle on a pad of soft rub- 

 ber. 



For examination of the etherized flies a hand lens may be used, but 

 a wide-field binocular microscope is much more efficient. For ordinary 

 genetic work a magnification of about 16 diameters is used. Under this 

 power it is easy to work rapidly for long hours without eye strain or 

 undue loss of efficiency from the smallness of the field that comes with 

 greater magnifications. 



A plate of white glass resting on the microscope stage furnishes a good 

 and convenient background for examining the flies. An ordinary desk 



