Ans-1) As the blastocyst reaches the final steps in the implantation process into the inner lining of the uterus, it evolves into a structure called an embryo. This is the time when internal organs and external structures develop. The mouth, lower jaw, throat are emerging, while the blood circulation system starts its evolution and a heart tube is created. The ears arise and arms, legs, fingers, toes, and eyes are being shaped. The brain and the spinal cord are already formed, while the digestive tract and sensory organs start their development. The first bones are replacing the cartilage. After ten-twelve weeks of pregnancy, the embryo moves into the final stage of development, a fetus.
Problems with Embryo DevelopmentSevere problems with embryonic development can occur as early as the first 3 weeks. With so many internal organ systems and external structures beginning specialization and development in the embryo, the developing organism is particularly sensitive to damage from genetic abnormalities and environmental exposures. These genetic abnormalities can range from spontaneous genetic mutations, to improper chromosome arrangement that can potentially affect the development of important structures like the heart or brain.
Alongside genetic abnormalities, any number of environmental factors (malnutrition, infections, disease, toxic exposures) can have an effect on genetic expression potentially proving to be lethal to the developing embryo.
Ans-2) The female tailed frogs then lay their fertilized eggs underneath rocks in streams. Some other frogs that have internal fertilization give birth to miniature frogs, or "froglets." But L. larvaepartus is the only species known to give birth to live tadpoles, the researchers said.