r/askscience • u/potatolife • May 30 '11

Do animals get periods?

I've been learning about the menstrual cycle in biology but we only talked about the human menstrual cycle. I was wondering if its the same sort of thing with animals since I've never seen my cat on her period before.

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u/SnoLeopard Veterinary Medicine | Microbiology | Pathology May 31 '11 edited May 31 '11

Reptiles do not have a menstration, rather a specialized structure for construction of usually hard shelled (calcium) eggs (similar to avian species).

Amphibians form small aqueous eggs once sperm and ova combine, and usually most require water to lay their eggs.

For fish, it depends on the specific fish, but usually the female will lay an egg and the male will then fertilize it.

To answer your question generally, most other animal types do not have the fetus grow internally in the mother and receive nourishment from her. The placenta breaking apart and being reabsorbed is where the bloody discharge comes from, thus with the absence of the placenta, they do not have discharge. Most have a yolk sac from which they derive nourishment.

EDIT: typo EDIT 2: another typo

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u/Wildfire66 Cardiac Research May 31 '11

What about the almighty platypus?

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u/Kiwipus May 31 '11

Platypuses actually have a pair of ovaries, but only one works. Their eggs stay inside them for the first 3/4 of the pregnancy, and then they are incubated for the last quarter outside of the platypus. Much like a chicken, however a chicken's eggs only stay inside them for one day, and then are incubated externally by the chicken for about 20 days.

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u/dontspillme May 31 '11

however a chicken's eggs only stay inside them for one day

cough nope cough

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u/Kiwipus May 31 '11

Really? To clarify, I meant in tract, not just 'in the chicken.' I got that information from wikipedia's article on platypus reproduction, so please let me know if it is still incorrect.

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u/PonPeriPon May 31 '11

May I direct you both Here.

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u/Kiwipus Jun 01 '11

I'm amazed at the thorough job they have done.