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Across 1. protects and surrounds the embryo 4. reproductive strategy in which the embryo develops within the mother's body 7. allows gas exchange with outside environment 8. reproductive strategy in which the embryos develop outside the mother's body 13. organism that regulates its body temperture by exchanging heat with its environment. 14. holds the waste material as the embryo grows 15. reptiles that have no temporal holes 17. gland that produces milk 20. collection of blood vessels that carries blood between the lungs and the heart 21. mammal that gives borth to live young that have completed fetal development 22. ectotherm that is covered with dry scales, breathes with lungs, and reproduces by laying eggs 23. reptiles that had one hole in each temporal region 24. surface whose shape moves air faster over the top than underneath it, allowing for flight

Down 2. mammal whose young complete fetal development in the mother's external pouch 3. mammal whose offspring complete development in laid eggs 5. collection of blood vessels that carries blood between the heart and the rest of the body, except for the lungs 6. found in birds reduces weight without compromising strength 9. complex structures made of keratin and provide insulation to maintain body temperature 10. organism that produces its own heat through metabolic processes 11. endothermic organism that has hair, mammary glands, bones in the ear that allow for hearing and a jaw for chewing 12. contains the nutrient supply for the growing embryo 14. oldest undisputed fossil bird 16. air-filled space that connects to a bird's lungs, aiding in breathing 18. reptiles that have two holes in each temporal region 19. long, flat bone that connects the ribs in front of the chest and to which the chest muscles attach