Summary. Extratesticular sperm maturation in the echidna mainly occurs in the initial segment of the ductus epididymidis. The process involves the development of motility, migration and loss of the cytoplasmic droplet, a decrease in permeability to Congo red and the formation of sperm bundles. The spermatozoa are supported in the bundles by a matrix of electron-dense material; the bundles are very motile in undiluted samples of luminal fluids.
Micropuncture studies of anaesthetized echidnas showed that the ductuli efferentes absorb 74% of the fluid and 46% of the soluble protein that enters them. The initial segment of the ductus epididymidis absorbs 83% of the fluid which enters it, and its secretions increase the concentration of protein in luminal fluid by 107%. Denatured, linear-gradient polyacrylamide gel electrophoresis of micropuncture samples showed that 1 protein (apparent Mr = 100 500) which is not present in blood plasma is present in rete testis fluid, and a glycoprotein which is present in rete testis fluid (apparent Mr = 78 500) is absorbed by the ductuli efferentes. Six proteins which are not present in blood plasma are secreted into the initial segment of the ductus epididymidis; 5 are glycoproteins (apparent Mr = 48 500, 39 000, 32 000, 20 500 and 19 000) and one (apparent Mr = 82 500) is not. The most prominent electrophoresis bands corresponded to the glycoproteins with apparent molecular weights of 48 500, 20 500 and 19 000.
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