Treatment of immature and mature epididymal spermatozoa with SDS and DTT reveals differences in the structural character of their respective tail organelles as a function of their maturity, which are not apparent in untreated spermatozoa. The response of mature sperm tails of rat, rabbit and other mammals to these reagents indicates that the segmented connecting pieces, the coarse outer fibers, the outer membrane of the mitochondrion and the fibrous sheath of the principal piece, as well as the relationships between these organelles, are stabilized highly by intermolecular SS crosslinks. The disruption of these structures by SDS alone in caput epididymal spermatozoa, however, implies their stabilization by disulfide bonds during sperm passage through the epididymis. Hence the pattern of flagellar beat seen typically in mature epididymal or ejaculated spermatozoa is probably determined by post‐spermiation changes in the structural as well as in the metabolic properties of the tail organelles.

In similar studies of a wide variety of sub‐mammalian species, the sperm tails fell into two broad classes. The “simple” tail, a plasma membrane enclosing only mitochondria and microtubule doublets (teleosts, frog, chicken and pigeon), disappeared immediately in SDS, though a partial SS dependent stability was inducible in the microtubules of teleost sperm tails. In the second class, the coarse fibers, arrayed as a nine‐membered ring (octopus, snake, lizard, turtle and sparrow) or otherwise (skate, newt), and the fibrous sheath (snake, lizard) also are stabilized by SS bonds, as is the undulating membrane of the urodele sperm tail.

Since the sperm mitochondria in all sub‐mammalian species were totally disrupted by SDS alone, an extreme SS dependent stability of the outer mitochondrial membrane may well be a feature unique to mammalian spermatozoa.