Reproduction. The female lays a single soft-shelled, leathery egg 22 days after mating, and deposits it directly into her pouch. An egg weighs 1.5 to 2 grams (0.05 to 0.07 oz) and is about 1.4 centimetres (0.55 in) long. While hatching, the baby echidna opens the leather shell with a reptile-like egg tooth.