The alien species known as the Grakk have a unique circulatory system that is comprised of a network of iridescent, glow-in-the-dark tubes that crisscross their bodies. These bioluminescent tubes are not only aesthetically pleasing to behold, but also serve as a vital component in their ability to regulate body temperature and circulate life-giving oxygen.
Chapter 4: Exploring the Alien Muscular System Chapter 5: Alien Skeletal Systems: A Study of Support and Structure