The gross anatomy of the alimentary canal and malpighian tubules of Agallia constricta (Van Duzee) is described, as well as the histology of their various regions. Rickettsia-like microorganisms and carbonates were found in the midgut. Each salivary gland, consisting of a principal 4-lobed gland and an accessory gland, contains 5 different types of acini. In the male reproductive system there are a pair of testes, each with 6 follicles, a pair of vasa deferentia, and a median ejaculatory duct, plus a pair of accessory glands. Each ovary of the female system is made up of 6 ovarioles, each consisting of terminal filament, germarium, vitellarium, and pedicel. The calyx connects the ovarioles with the lateral oviducts and these open to a common oviduct leading to the genital chamber; 2 small accessory glands and a paragenital gland are present. The central nervous system comprises 4 ganglionic masses: the brain, the subesophageal ganglion, the prothoracic ganglion, and the fused ganglia of mesothorax, metathorax, and abdomen; nerves from these various ganglia innervate the different organs. The circulatory system consists of a dorsal vessel, formed by a 7-chambered heart in the abdomen and an aorta extending from the heart into the head. What appear to be accessory pulsatile organs occur in the dorsal part of the abdomen and in each tibia near the femur. Each of the 2 mycetomes is an isolated structure in the anterior part of the abdomen, appressed laterally to the integument. The fat-body, surrounding all organs, is present in the head, thorax, and abdomen, but is most plentiful in the abdomen.