148 Invertebrate Zoology. 



call the attention of the instructor. An objective may be 

 ruined by being wiped with a dirty cloth. If, through acci- 

 dent, fluid runs on to the stage of the microscope, be sure 

 that it is all carefully removed from around the sub-stage. 

 Be especially careful of acids, and do not let them long 

 stand under the objective. Never wet the mirror. Do not 

 allow the instrument to stand in strong sunlight. Always 

 dust and put the instrument away after using. 



D. 



DIRECTIONS FOR DISSECTION. 



VERY small objects are studied by " teasing," which con- 

 sists of gently tearing them apart under a lens, or of placing 

 them under a cover-glass and tapping the cover lightly with 

 a needle, the result being observed under the compound 

 microscope. All teasing should be done while the object is 

 covered with liquid, generally water, glycerine, or alcohol. 



With somewhat larger animals the small scissors, scalpel, 

 and tweezers may be used, the object being pinned out 

 under water. As the water becomes cloudy it should be 

 renewed, or the cloudy portions may be removed with the 

 large bulb-pipette. 



It is only the larger animals that are ordinarily dissected 

 without being flooded with water. The sponge should be 

 freely used and, if possible, the animal should be frequently 

 placed under the tap. 



Nerves may generally be more easily separated from the 



