We learn more about the merfolk's anthropology. When a merbaby is born in the matriarch society, the mermen take the baby back to the colony so that they may teach it how to survive and hunt in the ocean. The mother does not see the child again until it reaches a mature age. Another thing is that the mermen trigger a different hormonal response in the young, affecting their development.
Maddie and Robb find the deceased half-transformed mermaid in the warehouse of the Marine Research Center.
Ben starts documenting his aquatic stem cell experimentation in video journals. He describes the physiology changes he's experienced: heightened senses, accelerated healing, increased endurance, and an increased lung capacity; he was able to hold his breath underwater for more than 10 minutes.
Katrina joins Tia's colony after being given an ultimatum. Her mermaid form transitions and now bears the same physiological appearance as Tia.
Maddie: "Ryn, what made you come back so soon? Is it Tia?"
Ryn: "No. I want my baby to learn about sea and land, to know both worlds. Like I do. I want you to show me how to be a mother on land."