An incubator is a device that provides controlled conditions to hatch eggs artificially. It is important in supplying heat for embryo development, ensuring that the eggs are kept at a constant temperature, humidity and ventilation. The temperature supplied by the incubator is critical for the embryo development and survival of the chick. Therefore, an incubator is crucial in providing the right conditions for the eggs to hatch into healthy chicks. Thus, the correct option is "heat for embryo development".