The electron microscope has been used to determine the characteristic dimensions and the distribution of the dry mass in bull spermatozoa. The most important result is that all characteristic data are occurring in logarithmic distributions. Furthermore, no correlation between such parameters as head weight and tail weight or head length and tail length was found. The occurrence in logarithmic distributions and the non-correlation of parts in the assembly of a spermatozoon are considered to reflect significant biologic principles. Methodologically, a new procedure is added to quantitative electron microscopy permitting the recording of the mass cross-section (total mass per unit length) of an object. This approach makes possible determinations of the distribution and the total mass of very long and narrow structures.