If you looking through a microscope at freshly prepare wet mount and see several perfect circle that are completely clear surrounding specimen, these are likely air bubbles. Air bubbles can be introduced into a wet mount preparation when the coverslip is placed on the slide, or they can be created by the movement of the slide or coverslip. Air bubbles can interfere with the observation of the specimen, and they can also cause the specimen to move around on the slide. To remove air bubbles, you can gently tap the coverslip with a pencil eraser or you can use a needle to pop the bubbles.