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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Gravid female boa 42 days after ovulation. An embryonic vesicle 10.2 mm in diameter, surrounded by a large anechoic area, is clearly visible. The outer membrane is instead hyperechoic. Phase recognized in 100% of females who gave birth to live and viable offspring.