1. Schistocerca gregaria Forsk. possesses about 250 Malpighian tubules arranged in twelve groups, situated dorso-laterally, laterally, ventro-laterally, and in the six intervening positions around the posterior end of the mid-gut. The gut forms an expanded ampulla at the point of entry of each group.
2. Each tubule is composed of five rows of cells, spirally arranged. Upper and lower segments are present, as in Rhodnius (Wigglesworth, 1931), the former very short. There is also a spiral trachea.
3. Tubules arise in seven generations, two in the embryo and one in each of the five nymphal instars. The first embryonal generation is composed of six primary tubules, the second of twelve embryonal secondaries. In the other five a variable number of nymphal secondaries is added, with means of 25, 51, 88, 63, and 6 respectively. The six primary tubules are attached distally to the rectum, the embryonal and first and second instar secondaries pass forwards, the fourth and fifth instar secondaries pass backwards, and the third in both directions.
4. The development of any one tubule comprises a period of initiation, a period of mitosis and elongation, and a period of differentiation. The first is restricted to the first few days of the particular stadium, the second takes place throughout the stadium, and the last throughout the life of the tubule.
5. The secondary tubules are arranged in an arc round the periphery of the ampulla. These arcs are perfectly symmetrical, the tubules arising alternately left and right of the mid-line during all the nymphal stages.
6. Tubule buds formed late in the period of initiation may cease to develop until the corresponding phase of the succeeding instar is reached.
7. The origin of tubules from a posterior interstitial ring and its relation to the interpretation of insect gastrulation and the nature of nymphal developmental cycles is discussed.