"Organ" - what is it, definition of the term
A distinct anatomical unit formed by coordinated tissues that together execute a specific physiological function within a multicellular organism, integrating cellular processes, maintaining homeostasis, and interacting with other bodily systems.
Detailed information
Ticks, bugs, lice, and fleas possess highly specialized internal structures that enable hematophagy, reproduction, and survival on host organisms. Their digestive tract consists of a foregut that channels ingested blood to a midgut where enzymatic breakdown occurs, followed by a hindgut that expels waste. Salivary glands in all four groups secrete anticoagulant and anesthetic compounds, facilitating prolonged feeding without detection. Respiratory exchange is achieved through a tracheal system that delivers oxygen directly to tissues, eliminating the need for a circulatory pump.
Reproductive anatomy varies among the groups:
- Ticks: females contain a single, enlarged ovary that produces thousands of eggs after a blood meal; males have paired testes and a spermatophore‑producing accessory gland.
- Bugs (Hemiptera): females possess paired ovarioles within a common ovary, while males feature paired testes and seminal vesicles.
- Lice: females carry a tubular ovary with a single oviduct; males have paired testes connected to a vas deferens.
- Fleas: females have a pair of ovaries each linked to a short oviduct; males exhibit paired testes and a well‑developed accessory gland.
Excretory function is performed by Malpighian tubules that filter hemolymph and deposit waste into the hindgut. Nervous control centers are concentrated in a ventral ganglion chain, which coordinates sensory input from antennae, palps, and mechanoreceptors. Muscular layers surrounding the body wall enable locomotion and attachment to hosts.
These internal components operate in concert to support the parasitic lifestyle of each arthropod, ensuring efficient nutrient acquisition, reproduction, and adaptation to the host environment.