Friday, May 12, 2006


Placental mode of reproduction is a process that occur in mammals, “is a temporary organ that develop during pregnacy”.[1] The growing embryo connects with the uterus through umbilcal cord to the mother,in this process the fuetus gets feed from the blood of the mother.the embryo grow inside the womb of the mother and it takes 12 months period for gestation. while the marsupial mode develop the yolk sack and it have short period of gestation, the embryo of the marsupial do not develop inside the womb of the species.[1]

Marsupials develops a pouch that they used to carry their early infant, this pouch develops in the belly of the species. “where the infant crawls ups and attach itself to the nipple for feeding, it can stays acttached to the nipples for period until it can pass the stage where it can live its mothers pouch. They will only returns to its mother for warmth and nourishment”.(2)[3]

During reproduction placental mammals develops placenta that protects the fetus from their mother s immune system. “while in marsupials they does not develop a complex of fetus, because they does not need any protection for the fetus from the immune system that the mother have”.[2]

Marsupials mode of reproduction and placental mainly differ interms of gestation period. In marsupials it takes short period, close to twelve days of the embryo of marsupials in the reproductive track. but this also influence by the type of egg yolk. while the placenta gestation takes takes 9 months , this occurs because the embryo of placental mammals need to be fully developed before birth. But if the placental mammals give birth before time,the fetus become prematurely and it will need care which is similar to marsupials.[3]

This two mode of reproduction also differ in the way their embryo develops,in marsupials the embryo is separeted from the body of the mother, while in placental the embryo is connected to the get all the support from nutrient ,oxygen through blood.marsupials only feed its fetus for short period and then start to breast feed the infant.[2]

Difference also seen when the placental mammals are pregnant the process of oestrus cycle does not happen until the end of pregnancy. Whereas in marsupials the oestrus cycle does not stop it takes place. “In marsupial the ovarian inhibition is mediated by lactation or suckling stimulus. These regulatory modifications are important because the baby will no longer be carried internally so negative feedback stimulus from the presence of the infant must come from nursing activity”.[3]

Mating system also differ and this can determine the mode of reproduction. in marsupial is different through out the year. Some species are single and they only come together to mate and this pattern of social behaviour reflect promiscuous mating systems.while in placental after mating male and female take time together, and this sometimes depend on the type of species.some males takes care of their infant.

In conclusion mode of reproduction differs with type of species and also the size of the species involve to the way in which species reproduce. Species that reproduce by placental must have big body as they have to carry the embryo for couple of months, while those with small bodies do not carry embryo in their belly they reproduce by marsupials they have to carry infant for short period,which will enable them to move because they have small bodies.


1. Wikipedia contributors. Placenta [Internet]. Wikipedia, the Free Encyclopedia; 2006 May 15, 13:52 UTC [cited 2006 May 10]. Available from:

2. Wikipedia contributors. Marsupials [Internet]. Wikipedia, the Free Encyclopedia; 2006 May 19, 22:51 UTC [cited 2006 May 10]. Available from:

3. Ashcraft.C.W. Marsupial Evolution And Post Flood Migration.[Internet]cited 2006-May-10] Available from:

Mr Elelwani Muanalo
NISL- Ecological Informatics Student
CSIR Pretoria
Tel: +27 12 841 2133
Fax: +27 12 842 7024.
My bloger URL:


  • You have a nice style of writting but the facts are not correct. Like in second paragraph you say marsupilas lay eggs no they don't! They practice internal fertilisation and the egg develops in the mothers womb.

    By Blogger Vincent, at May 12, 2006 4:17 PM  

  • Please reference every paragraph.

    Your references to gestation periods referred to specific organisms. You needed to give the organisms' names.

    How big are kangaroos? They are marsupials.

    By Blogger Gwen, at May 26, 2006 2:08 PM  

Post a Comment

<< Home