Question

Differentiate between

(a) oestrus and menstrual cycles

(b) ovipary and vivipary

Cite an example for each type.

Answer 1

Occurrence

Oestrus cycle occurs mostly in the reproductive system of female non-primate mammals. Menstrual cycle occurs only in the reproductive system of female primates.

Description

Oestrus cycle consists of a short period of oestrous or heat followed by an anoestrus or passive period. Menstrual cycle consists of menstruation, the follicular phase, ovulation and the luteal phase.

Endometrium

The broken endometrium is reabsorbed by the uterus. Thus bleeding does not occur during the oestrous cycle. The broken endometrium is shed off from the uterus and bleeds out through vagina during the menstrual phase.

Sexual activity

Female non-primate mammals are sexually active only in the ovulation period of the oestrus cycle. Female primates are sexually active throughout the menstrual cycle.

Mating

Copulation happens in the heat season only in animals undergoing an oestrous cycle. Copulation takes place in any season in animals undergoing menstrual cycle.

Examples

Oestrus cycle occurs in horses, cows, pigs, dogs etc. Menstrual cycle occurs in apes, monkeys, humans etc.

Summary

Criteria	Oestrus cycle	Menstrual cycle
Occurrence	Female non-primate mammals	Female primate
Description	Consists of a short period of oestrous or heat followed by an anoestrus or passive period	Consists of menstruation ,the follicular phase, ovulation and the luteal
Endometrium	The broken endometrium is reabsorbed by the uterus	The broken endometrium is shed off from the uterus and bleeds out through vagina
Sexual activity	Female non-primate mammals are sexually active only in the ovulation period	Female primates are sexually active throughout the menstrual cycle
Mating	Heat season only	Any season
Examples	Horses, cows, pigs, dogs	Apes, monkeys, humans

Definition

Ovipary is the phenomenon of laying fertilised or unfertilised eggs by female organisms. Vivipary is the phenomenon of giving birth to young ones by female organisms.

Embryogenesis

In case of oviparous animals, the zygotes are developed outside the body, protected from the external environment by calcareous shells. The young ones emerge from the egg after a period of incubation. The zygote is protected inside the female body and develops into young ones in case of viviparous animals.

Nourishment

The eggs obtain nourishment from the yolk in oviparous organisms. The embryo obtains the nourishment from the mother’s body in viviparous organisms.

Survival rate

Rate of survival of the eggs is low in offspring of oviparous animals as they are prone to harsh environmental conditions. Chances of survival are high in the offspring of viviparous animals as the development takes place inside the mother’s body.

Examples

Ovipary is observed in reptiles, birds and amphibians. Vivipary is observed in most mammals like cows, horses, dogs, lions and humans.

Summary

Criteria	Ovipary	Vivipary
Definition	Penomenon of laying fertilised or unfertilised eggs by female organisms	Phenomenon of giving birth to young ones by female organisms
Embryogenesis	Outside the body of female	Inside the body of female
Nourishment	From the yolk	From the mother’s body
Survival rate	Low	High
Examples	Reptiles, birds and amphibians	Most mammals like cow, horse, dog, lion and humans