mesoderm

"Muscle consists largely of actin and myosin filaments."

"The development of this story has been slow."

"The dry-stone wall used a large, flat through to support the top stones. "

"The scientist studied the embryonic development of the frog. "

"The delicate tissue paper wrapped the fragile antique doll. "

"The scientist studied the embryo to understand how the early stages of development occur. "

"After the first coat of paint dried, he applied another layer."

"The farmer's fields produced a bountiful harvest of tomatoes this year. "

"The circulatory system of the classroom heating vents was poorly designed; one side got excessively hot, while the other remained chilly, resulting in an uneven distribution of warmth. "

"We saw the internal compartments."

"A cat is an animal, not a plant. Humans are also animals, under the scientific definition, as we are not plants."

"The biology textbook explained that a human, being an animal developing from an embryo with three distinct tissue layers, is classified as a metazoan. "