Abstract
Summary
Fresh, unstained and unfixed samples of sperm from many fertile bulls studied under the electron microscope have shown that the anterior portion of the sperm head is always enveloped by a protoplasmic cap which appears damaged or disappears altogether if sperm are stained or fixed. This suggests that, contrary to results obtained with the optical microscope, the protoplasmic cap is not a sign of immature or abnormal sperm but is typical of normal sperm when these are examined without being exposed to solvents usually present in stains.
The tails end in a brush consisting of many free and very long filaments. Breaks in the main or end pieces of the tail have also shown flared brushes which make it seem likely that the axial filament consists of a bundle of fine fibers rather than a single relatively thick thread.
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