The Digestive Apparatus of a Beetle
The Annulosa and Mollusca are furnished with a distinct alimentary canal that does not open into the body cavity. In most cases, the digestive canal communicates with the outer world by two-openings- a mouth and an excretory aperture. The annulosa system is demonstrated in the digestive apparatus of a beetle.
Cutter, Calvin First Book on Analytic Anatomy, Physiology and Hygiene, Human and Comparative (Philadelphia: J. B. Lippincott & Co., 1875) 72