Editing Platypus (section)

=== Reproduction ===
[[File:Ornithorhynchus anatinus - nest with eggs - MUSE.JPG|thumb|Platypus's nest with eggs (replica)]]

The species has a single [[breeding season]] between June and October, with some local variation.<ref name="EPA" /> Investigations have found both resident and transient platypuses, and suggest a [[Polygyny in animals|polygynous]] mating system.<ref name="AJZ2">{{cite journal|journal=Australian Journal of Zoology|title=Aspects of Lactation in the Platypus, ''Ornithorhynchus anatinus'' (Monotremata), in Waters of Eastern New South Wales|author=Grant, T. R. |author2=Griffiths, M. |author3=Leckie, R.M.C. |volume=31|issue=6|pages=881–9|doi=10.1071/ZO9830881|year=1983}}</ref> Females are believed to become sexually mature in their second year, with breeding observed in animals over nine years old.<ref name="AJZ2"/> During [[Copulation (zoology)|copulation]], the male grasps the female's tail with his bill, wraps his tail around her, then grips her neck or shoulder, everts his [[penis]] through his [[cloaca]], and inserts it into her [[urogenital sinus]].<ref>{{Cite book |last=Grant |first=Tom |url=https://books.google.com/books?id=bu8rIm-TdqwC&dq=platypus+copulation&pg=PA17 |title=Platypus |date=2007-10-02 |publisher=Csiro Publishing |isbn=978-0-643-10127-2 |language=en}}</ref> He takes no part in nesting, living in his year-long resting burrow. After mating, the female constructs a deep, elaborate nesting burrow up to {{convert|20|m|ft|round=5|abbr=on}} long.<ref name="ADW">{{cite web |url=http://animaldiversity.ummz.umich.edu/site/accounts/information/Ornithorhynchidae.html |title=Family Ornithorhynchidae (platypus) |author1=Anna Bess Sorin |author2=Phil Myers |name-list-style=amp |publisher=University of Michigan Museum of Zoology |year=2001 |access-date=24 October 2006 |archive-date=10 April 2011 |archive-url=https://web.archive.org/web/20110410142645/http://animaldiversity.ummz.umich.edu/site/accounts/information/Ornithorhynchidae.html |url-status=live }}</ref> She tucks fallen leaves and reeds underneath her curled tail, dragging them to the burrow to soften the tunnel floor with folded wet leaves, and to line the nest at the end with bedding.<ref name="APC" />

The male platypus has [[penile spines]] and an asymmetrical [[glans penis]], with the right side smaller than the left.<ref>{{Cite book |last1=Vogelnest |first1=Larry |url=https://books.google.com/books?id=4d6VDwAAQBAJ&dq=platypus&pg=PA64 |title=Current Therapy in Medicine of Australian Mammals |last2=Portas |first2=Timothy |date=2019-05-01 |publisher=Csiro Publishing |isbn=978-1-4863-0752-4 |language=en}}</ref> The female has two [[Ovary|ovaries]], but only the left one is functional.<ref>{{Cite book |last1=Vogelnest |first1=Larry |url=https://books.google.com/books?id=p8cDEAAAQBAJ&pg=PA107 |title=Medicine of Australian Mammals |last2=Woods |first2=Rupert |date=18 August 2008 |publisher=Csiro Publishing |isbn=978-0-643-09797-1 |language=en |access-date=27 April 2024 |archive-date=25 May 2024 |archive-url=https://web.archive.org/web/20240525044226/https://books.google.com/books?id=p8cDEAAAQBAJ&pg=PA107#v=onepage&q&f=false |url-status=live }}</ref><ref name="EC" /> She lays one to three (usually two) small, leathery eggs (similar to those of reptiles), about {{convert|11|mm|in|frac=32|abbr=on}} in diameter and slightly rounder than bird eggs.<ref name="BSED">{{cite journal|journal= Philosophical Transactions of the Royal Society B: Biological Sciences|title=Early development and embryology of the platypus|author=Hughes, R. L. |author2=Hall, L. S. |volume=353|issue=1372|pages=1101–14|date=28 July 1998|pmid= 9720108|pmc= 1692305 | doi = 10.1098/rstb.1998.0269}}</ref> The eggs develop ''[[Uterus|in utero]]'' for about 28 days, with only about 10 days of external [[Avian incubation|incubation]] (in contrast to a chicken egg, which spends about one day in tract and 21 days externally).<ref name="EC" /> The female curls around the incubating eggs, which develop in three phases.<ref name="RS2" /> In the first, the [[embryo]] has no functional organs and relies on the [[yolk sac]] for sustenance, until the sac is absorbed.<ref>{{cite web|title=Ockhams Razor|work=The Puzzling Platypus|url=http://www.abc.net.au/radionational/programs/ockhamsrazor/the-puzzling-platypus/3492688|access-date=2 December 2006|date=20 July 2001|archive-date=9 August 2017|archive-url=https://web.archive.org/web/20170809103030/http://www.abc.net.au/radionational/programs/ockhamsrazor/the-puzzling-platypus/3492688|url-status=live}}</ref> During the second phase, the digits develop, and in the last phase, the [[egg tooth]] appears.<ref name="RS2">{{cite journal|journal=Philosophical Transactions: Biological Sciences|title =The development of the external features of the platypus (''Ornithorhynchus anatinus'')|author=Manger, Paul R. |author2=Hall, Leslie S. |author3=Pettigrew, John D. |volume=353|issue=1372|pages=1115–25|date=29 July 1998|pmid=9720109|pmc=1692310|doi =10.1098/rstb.1998.0270}}</ref> At first, European [[natural history|naturalists]] could hardly believe that the female platypus lays eggs, but this was finally confirmed by [[William Hay Caldwell]] in 1884.<!--for wiring London and other such trivia see that article--><ref name="ABRS"/><ref name="PS"/>

Most mammal zygotes go through [[holoblastic]] cleavage, splitting into multiple divisible daughter cells. However, [[monotremes]] like the platypus, along with [[Sauropsida|reptiles and birds]], undergo meroblastic cleavage, in which the ovum does not split completely. The cells at the edge of the yolk remain continuous with the egg's cytoplasm, allowing the yolk and embryo to exchange waste and nutrients with the egg through the cytoplasm.<ref>{{cite journal|author=Myers, P. Z.|url=http://www.nature.com/scitable/topicpage/interpreting-shared-characteristics-the-platypus-genome-44568|title=Interpreting Shared Characteristics: The Platypus Genome|journal=Nature Education|volume=1|issue=1|page=462008|year=2008|access-date=26 March 2015|archive-date=4 March 2018|archive-url=https://web.archive.org/web/20180304124410/http://www.nature.com/scitable/topicpage/interpreting-shared-characteristics-the-platypus-genome-44568|url-status=live}}</ref>

Young platypus are called "puggles". Newly hatched platypuses are vulnerable, blind, and hairless, and are fed by the mother's milk, that provides all the requirements for growth and development.<ref>{{cite web|last1=Stannard|first1=Hayley J.|last2=Old|first2=Julie M.|title=Wallaby joeys and platypus puggles are tiny and undeveloped when born. But their mother's milk is near-magical|url=https://theconversation.com/wallaby-joeys-and-platypus-puggles-are-tiny-and-undeveloped-when-born-but-their-mothers-milk-is-near-magical-207726|publisher=The Conversation|year=2023|access-date=25 October 2023|archive-date=10 November 2023|archive-url=https://web.archive.org/web/20231110202925/https://theconversation.com/wallaby-joeys-and-platypus-puggles-are-tiny-and-undeveloped-when-born-but-their-mothers-milk-is-near-magical-207726|url-status=live}}</ref><ref>{{cite journal|last1=Stannard|first1=Hayley J.|last2=Miller|first2=Robert D.|last3=Old|first3=Julie M.|title=Marsupial and monotreme milk – a review of its nutrients and immune properties|journal=PeerJ|year=2020|volume=8|page=e9335|doi=10.7717/peerj.9335 |pmid=32612884 |pmc=7319036 |doi-access=free }}</ref> The platypus's [[mammary gland]]s lack [[teat]]s, with milk released through pores in the skin. The milk pools in grooves on the mother's abdomen, allowing the young to lap it up.<ref name="APC" /><ref name="EPA" /> After they hatch, the offspring are milk-fed for three to four months.

During incubation and weaning, the mother initially leaves the burrow only for short periods to forage. She leaves behind her a number of thin soil plugs along the length of the burrow, possibly to protect the young from predators; pushing past these on her return squeezes water from her fur and allows the burrow to remain dry.<ref name="QM">{{cite web|url=http://www.qm.qld.gov.au/inquiry/factsheets/leaflet0010.pdf|title=Egg-laying mammals|publisher=Queensland Museum|date=November 2000| access-date = 19 June 2009|archive-url = https://web.archive.org/web/20080722180447/http://www.qm.qld.gov.au/inquiry/factsheets/leaflet0010.pdf |archive-date = 22 July 2008|url-status=dead}}</ref> After about five weeks, the mother begins to spend more time away from her young, and at around four months, the young emerge from the burrow.<ref name="EPA" /> A platypus is born with teeth, but these drop out at a very early age, leaving the horny plates it uses to grind food.<ref name="Piper-2007">{{cite book |author-link=Ross Piper |first=Ross |last=Piper |title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals |url=https://archive.org/details/extraordinaryani0000pipe |url-access=registration |publisher=[[Greenwood Press (publisher)|Greenwood Press]] |year=2007 |isbn=978-0-313-33922-6 }}</ref>