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Platypuses can give a low growl when disturbed, and a range of vocalisations have been reported in captivity. [16] Size varies considerably in different regions, with average weight from 0.7 to 2.4 kg (1 lb 9 oz to 5 lb 5 oz); males have average length 50 cm (20 in), while females are the smaller at 43 cm (17 in). [21]
Egg size tends to be proportional to the size of the adult bird, [citation needed] from the half gram egg of the bee hummingbird to the 1.5 kg egg of the ostrich. Kiwis have disproportionately large eggs, up to 20% of the female's body weight. [ 18 ]
The mammals included are only viviparous (marsupials and placentals) as some mammals, which are monotremes (including platypuses and echidnas) lay their eggs. A marsupial has a short gestation period, typically shorter than placental. For more information on how these estimates were ascertained, see Wikipedia's articles on gestational age.
According to the observation of embryonic cells of egg, chromosome number of the itch mite is either 17 or 18. While the cause for the disparate numbers is unknown, it may arise because of an XO sex determination mechanism, where males (2n=17) lack the sex chromosome and therefore have one less chromosome than the female (2n=18). [29] [29] 32 ...
The only living mammals that lay eggs are echidnas and platypuses. In the latter, the eggs develop in utero for about 28 days, with only about 10 days of external incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally). [11] After laying her eggs, the female curls around them.
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At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird, [2]: 130 though the extinct elephant bird and some non-avian dinosaurs laid larger eggs.
Meroblastic cleavage occurs in animals whose eggs have more yolk (i.e. birds and reptiles). Because cleavage is impeded in the vegetal pole, there is an uneven distribution and size of cells, being more numerous and smaller at the animal pole of the zygote. [8] [9]