Electron Microscopic Studies of Spermatozoa I. The Morphology of the Spermatozoon of the Common Domestic Fowl (Gallus Domesticus)

Abstract

The morphology of the fowl spermatozoon, as revealed by use of the electron microscope and such technics as partial enzymic digestion and disruption with dist. water, is described in detail, and compared with that observable by light microscopy. The sperm head carries at its anterior extremity a spindle-shaped body, the apical spine, which normally is closely covered by a conical membranous cap. The apical cap, which has been overlooked by previous workers, may be detached by dilution of the semen with dist. water. It seems likely that these structures are intimately concerned in the penetration of the vitelline membrane during fertilization. The axial filament, which contains 9 L fibrils arising from the anterior distal centriole and 2 M fibrils, passes through the mid-piece and continues the full length of the tail, approaching 100 u in length. It is surrounded in the mid-piece by a number of granules, presumably of mitochondrial origin, which are arranged to give an appearance of bilaterally symmetrical segmentation. The mid-piece is externally surrounded by a delicate membrane easily disrupted in dist. water. There is no evidence for the presence of a spireme or other helically-wound structure in the mid-piece. In the tail, the axial filament is encased in an amorphous sheath, which decreases in thickness towards the tip of the tail and is easily disrupted by dist. water, allowing the axial filament to fray into 11 fibrils. Two of these fibrils are differentiated from the remaining 9 by their dimensions and greater susceptibility to dist. water. It is suggested that the 9 L fibrils constitute the locomotor organ of the sperm. It is possible that the 2 M fibrils function as a rudimentary nervous system. In direct contrast with the state prevailing in mammalian sperm, there is no helically-wound cord surrounding the axial filament in the tail. This seems to explain why the tails of fowl and of certain other sperm fray easily in dist. water, while those of mammalian sperm do not. Certain dilution phenomena are explained by the presence of an adsorbed layer of colloidal material, which is removable by great dilution or repeated washing of the sperm. The layer greatly modifies the rat of osmosis in hypotonic solns. There is no trace of a lipoid or other capsule external to the cell-wall, as has been postulated to explain similar protective phenomena occurring with other sperm.