Source question 63. Question 60 asks about the preceding passage as a whole. 59 59 61 62 63 life stage. In a sense, they grew younger. T. dohrnii has no brain or heart. After fertilization, a T. dohrnii egg develops into a free-swimming, ovoid larva. In time, the larva settles on the ocean floor and transforms into a mound of cells—a hydroid colony. Buds grow on the colony and develop into young jellyfish with the familiar bell-like shape and tentacles. These jellyfish then detach from the colony, and drift away reaching maturity in a few weeks. After Sommer’s discovery, studies confirmed that T. dohrnii’s life cycle is not a one-way street. An adult T. dohrnii, if stressed—by injury, disease, or even just old age, has the ability to revert to a hydroid colony. That colony can then create new jellyfish, which in turn can also revert to hydroid colonies. There’s no apparent limit to these perpetual cycles of metamorphic transformation. In the 1990s, journalists nicknamed T. dohrnii the “immortal jellyfish.” It is true that scientists have replicated all stages of T. dohrnii’s life cycle, but each individual T. dohrnii isn’t immortal. Although the cells of the adult are essentially recycled during its transformation, all the new jellyfish grow into separate organisms—albeit genetically equivalent ones.
