. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 1. Longitudinal section of the head. Galea capitis con- sists of an outer membrane {a) and an inner one (h), which continues down and lines a cavity in the tip of the head (c). Galea capitis has been forced off the head. On the surface of galea capitis there is an outer membrane approximating 50 A which continues down to the basal part of the head (d). Magnification 22,000. The inner membrane of the galea capitis forms a pocket lining an acrosomal cavity. At the bottom of this acrosomal cavity is seen a dens
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 1. Longitudinal section of the head. Galea capitis con- sists of an outer membrane {a) and an inner one (h), which continues down and lines a cavity in the tip of the head (c). Galea capitis has been forced off the head. On the surface of galea capitis there is an outer membrane approximating 50 A which continues down to the basal part of the head (d). Magnification 22,000. The inner membrane of the galea capitis forms a pocket lining an acrosomal cavity. At the bottom of this acrosomal cavity is seen a denser struc- ture. The cavity is otherwise filled by a structureless mass that continues into the mass filling up the space between the two galea capitis membranes, and which gives less contrast than the other parts of the head. We have sectioned several somewhat shorter heads in a sagittal or oblique plane and have found similar structures, but with acrosomal cavities larger and oval in shape. Discussion.—Galea capitis in human sperm is exceptionally delicate and fine in structure—so deli- cate, in fact, that up to now there has been doubt as to whether such a structure was present in mature sperm (cf. 5, 6, 12). Electron microscopists, too, have denied its existence in humans ( ref. 8). On a few of Retzius (9) pictures of mature human sperm one nevertheless discerns a contour just in front of the equator of the head, which would cor- respond to the rearmost boundary of a hood. Some irregularly shaped heads likewise suggest the presence of a galea in human sperm (cf. 3. plate I, figure 5), which may be hypertrophied relative to the head. Furthermore, Williams (13) is of the opinion that he has observed a loose galea in a single case. Phylogenetically the presence of galea in human sperm is a reasonable assumption. It has been pos- sible to prove the existence of a hood in a large number of animals from varying phylogenetic levels, though these hoods have been of diverse s
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