Housefly head. Stacked macrophotograph of the head of a housefly (Musca domestica). The image shows the compound eyes, the antennae with their arista (a sensory organ), the maxillary palpi and 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.