Origin, development and ultrastructure of boar spermatozoa with folded tails and with two tails.

Spermatozoa from the three epididymal regions (head, body and tail) of healthy and sexually mature boars have been examined by light microscopy, and scanning and transmission electron microscopy. The origin, development and external and internal morphologies of aberrant spermatozoa with folded tails and spermatozoa with one or two heads and two fused tails have been established. A count carried out in each region of the epididymis indicated that significant differences (P less than 0.01) exist in the frequencies of each type of malformation and the epididymal region from which the spermatozoa come. Spermatozoa with folded tails at Jensen's ring originate in the cauda of the epididymis from immature spermatozoa that have not ejected the distal cytoplasmic droplet. The plasma membrane which covers the main piece is fused with the membranes of the midpiece, the connecting piece and the head. The fibrous sheath deforms the mitochondrial sheath and is placed between the plasma membrane and the postacrosomal dense lamina. Spermatozoa with one head and two fused tails originate in the epididymal body from spermatozoa with one head and two unfused tails coming from the cephalic region of the epididymis. Spermatozoa with two heads and two fused tails originate in the cephalic region of the epididymis by head-to-head agglutination of two spermatozoa and later fusion of their tails. The frequency of spermatozoa with two fused tails increases as they progress through the epididymal duct. Their tails, parallel in monocephalic spermatozoa and helicoid in bicephalic spermatozoa, have two complete axonemal axes. In their midpiece, the mitochondrial sheaths of the two axes are fused, producing an 8-shaped sheath.