In other insects, such as the Gryllidae, the acroblast or Golgi body is single, as in Mammalia, and the acrosome is usually deposited very little outside its definitive position. If it is out of position it appears to migrate over the nuclear membrane. In all these cases the anterior centriole has already become fixed to the nucleus, and, so far as is known, does not move, and always constitutes the one fixed point in the long axis of the nucleus and cell. In Text-figs. 1–11, from stages 1–3, this almost universal simple type of acrosome formation is given. At stage 2 slight rotation of the nucleus, or short migration of the acrosome to its definitive position, has been assumed to occur, but it is certain that in the majority of cases migration upwards of the Golgi apparatus (acroblast) with its acrosome in stage 1 occurs. It is at this period also that the hitherto scattered mitochondria (M) pass down to the back or post-nuclear region. How these differential movements occur is unknown. In Text-figs. 4–7 is shown the curious case of Melanoplus differentialis discovered by M. Devine at the Argonne National Laboratory. In Text-fig. 4, the acrosome is deposited usually quite near the presumably fixed centriole (C), and therefore well away from its future position at the anterior end of the nuclear axis. Soon the Golgi apparatus parts from the acrosome, which now becomes detached from the nucleus, and is next found stuck to the cell wall opposite (Text-fig. 3). During its time on the cell wall, the acrosome causes the development of an extra-cellular cap (P), which later becomes part of the ripe spermatozoon acrosome. The subsequent stages which bring about the deposition of the acrosome in its definitive position on the nucleus are not fully understood, and there are several possible explanations. The important point that in all the cases known the anterior centriole (C) is fixed has been mentioned. This is assumed to be true, because once the centriole becomes adherent to the nuclear membrane, a reaction takes place in this region which produces the so-called centriole seat of Gatenby (1931). In other cases a pin or peg, is produced in this region, which would appear to anchor the centriole permanently. Thus some explanation of the ultimate arrangement of acrosome and centriole in the long axis of the nucleus must be advanced. In Text-fig. 6, there is, first, one explanation—namely, that the nucleus plus centriole and mitochondrial body all rotate to meet the acrosome. Re-orientation of the whole spermatid with reference to the testicular lumen presumably follows. A second possible explanation is that given in Text-fig. 7, where the acrosome and its outer cap (P) moves up to the anterior end of the cell: a small rectification of the position of the nucleus and acrosome or both would then bring the acrosome into its definitive position. It is interesting to note that the gryllid Nemobius sp., and Gryllus (Acheta), have the type of acrosome formation shown in Text-figs. 1–3, whilst the locustid Melanoplus differentialis, also an orthopteran, has the quite different system given in Text-figs. 4–7. Still another method of acrosome formation has now been found in the oligochaete Lumbricus by Gatenby and Dalton (1958), and is given in Text-figs. 8–11. In the spermatid, the usual Golgi apparatus plus acrosome (G, A) is found. In addition a small hollow sphere appears in this region (AL). This is the acrosome carrier anlage, which swells to form a bowl-like structure (Text-fig. 9) into the mouth of which passes the acrosome. The spermatid nucleus has become elongated (Text-fig. 10), marking a point of development at which in other spermatids, such as in Homo, Mus, Cavia, and Invertebrata in general, the acrosome has already become attached to the nucleus as in Text-fig. 3. It has been assumed by Gatenby and Dalton, that the bead of protoplasm containing the acrosome carrier now moves upwards and finally reaches a point where the acrosome can pass over to its correct position as in Text-fig. 11. Examination of stages 9–11 suggests that another explanation of the manner of arrival of the acrosome at the head of the cell might be put forward. If the anterior end of the cell elongated so as to leave the bead