Housefly head. Stacked macrophotograph of the head of a housefly (Musca domestica). The image shows one of the compound eyes, one of the two antennae with its arista (a sensory organ) and the mouthparts consisting of the retractable flexible proboscis with an enlarged fleshy tip, the labellum, a sponge-like structure with many grooves (pseudotracheae) sucking up fluids by capillary action.