Xenopus is a genus of frogs which are commonly used by developemental biologists as model genetic organisms in research.
Xenopus laevis and Xenopus tropicalis are the two most commonly used species in genetic research because of their large embryo size for ease in manipulation, generation of large numbers of eggs (ranging from 300 to 3000 depending on species) and most importantly, the relatively long time in external development of the embryo. This allows biologists to examine embryonic processes that are controlled by maternal mRNA which were deposited in the egg. Many significant embryonic processes occur prior to embryonic genome transcription which gives the oppurtunity for researchers to observe the effects of maternal mRNA on early embryo developement.  
. Xenbase. Introduction to Xenopus. Availiable at: http://xenbase.org/anatomy/intro.do (last accessed at 27.11.13)
. Trans-NIH Xenopus Initiative. Advantages of Xenopus as a Model for Biomedical Research. Availiable at: http://www.nih.gov/science/models/xenopus/advantages.html (last accessed at 27.11.13)