(1) Resembling muscle. (2) One of the fine, contractile, threadlike protoplasmic elements found in certain epithelial cells in lower animals. (3) A contractile part of retinal cones in certain fish and amphibia. In mammals, the myoid is the inner part of the inner segment of rods and cones; it contains microtubules, the Golgi apparatus, endoplasmic reticulum, and ribosomes, but no myofibrils. [myo- + G. eidos, appearance]