Aspects of the external and internal anatomy of the red velvet mite Allothrombium lerouxi Moss are reported from study of whoiemounts and serial sections. The scuta and genitalia of nymph and adult are described and figured, and the utilization of these structures as valid developmental characters is discussed. The respiratory system, digestive system, circulatory system and nervous system of the adult are described and figured; attention is drawn to the tendency of sorne authors to confuse saiivary ducts with respiratory structures.