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		Discussion The results of the foil procedure support the hypthesis that the heart morphogenetic fields in the axolotl are under regulative control. Morphogenetic fields are veryimportant in that they help determine how different organs in the axolotl develop (from the heart and gills to the limbs). The results of the study confirm this idea by showing that two hearts formed when an impermeable barrier was placed between the heart primordia. The movies show that the same axolotl had two hearts, one on each side of the body. After the bisection the two sides of the morphogenetic field were not in direct communication. As a result both heart primordia developed into a complete heart. If there had been no bisection, the heart field would have just developed into one heart. No embryos survived to stage 37 with fully developed hearts in the grafting procedure. There are a number of possible reasons for the deaths of the embryos. Being caught in the wells or agar of the surgical dishes could have irreparably injured the embryos. Only one case was documented in which an embryo was left in a well and grew there until it got stuck. This embryo was partially damaged when it was removed from the well. Injuries to the head regions may have been due to the agar. To prevent further possible damage, the embryos were transferred to agarless petri dishes as soon as they appeared sufficiently healed from surgery. This terminated the instances of embryos being damaged by the agar. If the embryos did not heal before they reached stage 29, they would begin to move and injure themselves, eventually causing themselves severe damage. Healing could have been disrupted if the grafts were composed of neural tissue. However, special care was taken to cut the graft from the non-neural, gill-forming ectoderm region on the lateral side of the donor embryo. Thus, while it is likely that the embryos did not heal from the surgery, it was presumably not due to the use of neural cells in the graft. By the second post operational day, some embryos were beginning to move independently and to react to external stimuli. Some were moving and getting caught in different areas of agar. This could have disrupted or damaged the graft in some way. When they could not heal, the embryos died and their bodies degenerated to the pools of unorganized cells seen in Figure 5B (J. Cebra-Thomas, personal communication, 2004). The failure of the embryos to develop fully functional hearts did not negate the value of this experiment. The methodology can be a useful tool for studying the types of regulation that occur in developing embryos. If the embryos had been moved to agarless dishes earlier, some of the injuries that may have contributed to the embryo death could have been avoided. Similarly, mistakes due to inexperience manipulating the microtools are very common and would be avoided if this experiment were repeated for practice. The incisions would be smaller, neater, and would therefore heal faster. Both of these changes would increase the survival rate and allow the embryos to develop far enough to display either regulative or autonomous development in the heart.