MadSci Network: Development

Re: How come frogs start as Tadpoles?

Date: Sun Feb 18 20:36:54 2001
Posted By: Irene Yan, Post-doc/Fellow, Vertebrate Embryology, Rockefeller University
Area of science: Development
ID: 979438984.Dv

That is a very good question.  Some frogs, in fact DO give baby frogs, in 
a process called DIRECT DEVELOPMENT where there is no free swimming 
tadpole stage.  Direct developing frogs can either be ovoviviparous or 
viviparous, depending if an egg is involved in the process or not.  
Oviparous means “egg-laying” (ovo means egg in Latin) and viviparous 
means “life-laying” (vida is life in Latin),  ovoviviparous would me a 
mixture of both.  Thus, the frogs can be subdivided according to their 
reproductive mode as:
1) oviparous:these are mostly aquatic, and because they live where water 
is abundant, their eggs will develop first in the swimming tadpoles that 
then metarmorphose into froglets. The Xenopus laevis  
( is an example of 
oviparous frog.
2) ovoviviparous: These frogs will lay eggs that when hatched give out 
tiny small froglets (quite cute actually, in my opinion).  Sometimes the 
eggs are not laid into the exterior environment, rather, the mother (and 
sometimes the father) will carry the eggs until gestation is over. An 
example of that would be the Golden Coqui from Puerto Rico 
html)  Nourishment during the whole period is provided by the egg yolk.  
3) viviparous: These are rare, and like mammals will produce live 
offspring, the young feed on oviductal secretions produced by the mother, 
but there is no placenta.  Most of the viviparous amphibians are 
salamanders.  Of the fogs, the African toad Nectophrynoides occidentalis 
is an example.
So, I hope that this answers your question.  Some frogs do actually start 
as baby frogs.  If you wish to know more about the different species of 
frogs, try these different websites:
lnd.shtml    This is a really fun sites with 
lots of frog facts http://la'sWho.html   A list with 
description of the amphibian families
tp://  This 
a site about a frog in Australia that gives birth through the mouth!  The 
baby froglets just crawl out of the mother’s mouth after 8 weeks of 

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