. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 5. Electron micrograph of a longitudinal section of a locust immature sperm head fixed in 1 % osmium tetroxide. to distinguish such gross characteristics as pairing of chromatids (fig. 4) both in transverse section (M) and longitudinal section (N). When thinner sections are used in order to obtain higher resolution the poor preservation makes interpretation almost impossible. Sperm and spermatid heads of the locust have been shown by birefringence studies and ultra-violet dichroism studies (1) to contain nuc
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 5. Electron micrograph of a longitudinal section of a locust immature sperm head fixed in 1 % osmium tetroxide. to distinguish such gross characteristics as pairing of chromatids (fig. 4) both in transverse section (M) and longitudinal section (N). When thinner sections are used in order to obtain higher resolution the poor preservation makes interpretation almost impossible. Sperm and spermatid heads of the locust have been shown by birefringence studies and ultra-violet dichroism studies (1) to contain nucleic acid mole- cules orientated along the axis of the head. It is, therefore, interesting to examine this material in the electron microscope after various fixatives in order to obtain some idea of the value of these fixatives in preserving chromatin fine structure. While we have not as yet been able to demonstrate structure in mature sperm heads, we have observed well defined and characteristic structure in the heads of sperma- tids. This structure in the most highly developed form we have been able to observe is shown in longitudinal section in fig. 5 where it appears as a large number of parallel lines of thickness about 70 A which are orientated along the axis of the head. The corresponding transverse section—which is from the same cyst in the follicle and so must represent the same stage of development — is shown in fig. 6 to be a large number (about 270 in this case) of tightly packed polygons. We interpret these sections to mean that the head contains a large number of parallel tubes orientated along its axis (3). At this stage of development the head is shrinking rapidly and at later stages this structure seems to become too tightly packed to be easily visible and the head appears structureless. At earlier stages of develop- ment we have observed that material first seems to aggregate into sheets and that these sheets then appear to wrap around each other to form t
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